@Phoenix06,

Good idea in any case - just strip it to the bone to see if and when the behavior goes away. Unfortunately that didn't lead to any success on my end this time. So here is a stand alone html file which reproduces the problem. Just change the Ext path if needed.

Thanks!
Brad

Code:
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
    <title>New Index Page</title>
    <link rel="stylesheet" type="text/css" href="ext-4.0.7/resources/css/ext-all.css" />


    <script src="ext-4.0.7/ext-all-dev.js" type="text/javascript"></script>


    <script type="text/javascript">


        Ext.onReady(function() {


            var sitesData =  { "records": 
                [
                    { "id": "142784","lat": "37.36390","lng": "-121.86493","type": "2~8","listTypes": "ERNS~GENERATOR~LUST","sitenames": "Frito-Lay Inc~FRITO LAY INC","siteName": "Frito-Lay Inc","riskLevel": "2","street": "650 N KING RD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CARIMSCA-00-1090~CARIMSCA-97-0642~CASCVWD1-06S1E33K01~NARCRA00-CAD981656721"},
                    { "id": "142965","lat": "37.36521","lng": "-121.86681","type": "2","listTypes": "LUST","sitenames": "Matos Auto Center","siteName": "Matos Auto Center","riskLevel": "2","street": "670 N King Rd","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608500876"},
                    { "id": "142979","lat": "37.36529","lng": "-121.86717","type": "2~4","listTypes": "HAZMAT~LUST","sitenames": "Matos Auto Center~Matos Auto Towing/Transpo","siteName": "Matos Auto Center","riskLevel": "2","street": "670 N King Rd","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASAJOSE-1086~CASAJOSE-1087~CASCVWD1-06S1E33K02"},
                    { "id": "142872","lat": "37.36460","lng": "-121.86720","type": "1","listTypes": "CSL","sitenames": "PIED PIPER THE","siteName": "PIED PIPER THE","riskLevel": "1","street": "686 KING RD N","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACSLLIS-T0608591638"},
                    { "id": "142781","lat": "37.36386","lng": "-121.86555","type": "2","listTypes": "LUST","sitenames": "Frito-Lay Inc","siteName": "Frito-Lay Inc","riskLevel": "2","street": "650 N King Rd","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608500650"},
                    { "id": "142440","lat": "37.36130","lng": "-121.86666","type": "2","listTypes": "LUST","sitenames": "Lenfest Associates","siteName": "Lenfest Associates","riskLevel": "2","street": "697 Lenfest Rd","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608500829"},
                    { "id": "142396","lat": "37.36098","lng": "-121.86572","type": "8","listTypes": "ERNS","sitenames": "Unknown","siteName": "Unknown","riskLevel": "8","street": "591 king rd parking lot area","city": "SAN JOSE","state": "CA","ZIP": "95116","siteids": "CARIMSCA-1995-8510"},
                    { "id": "142497","lat": "37.36172","lng": "-121.85407","type": "8","listTypes": "ERNS","sitenames": "Unknown","siteName": "Unknown","riskLevel": "8","street": "2050 McKee Road, Rancho Verdi Apts.","city": "SAN JOSE","state": "CA","ZIP": "95116","siteids": "CARIMSCA-01-0281"},
                    { "id": "142475","lat": "37.36153","lng": "-121.85549","type": "2","listTypes": "LUST","sitenames": "7-Eleven #15946","siteName": "7-Eleven #15946","riskLevel": "2","street": "2044 McKee Rd","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASCVWD1-06S1E34N01"},
                    { "id": "142410","lat": "37.36108","lng": "-121.85544","type": "2","listTypes": "LUST","sitenames": "7-Eleven #15946","siteName": "7-Eleven #15946","riskLevel": "2","street": "2044 McKee Rd","city": "SAN JOSE","state": "CA","ZIP": "95116","siteids": "CALUSTCA-T0608500076"},
                    { "id": "143215","lat": "37.36666","lng": "-121.86918","type": "2","listTypes": "LUST","sitenames": "De Jesus Store","siteName": "De Jesus Store","riskLevel": "2","street": "796 N King Rd","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASCVWD1-06S1E33L02"},
                    { "id": "143227","lat": "37.36675","lng": "-121.86855","type": "2","listTypes": "LUST","sitenames": "PRIVATE RESIDENCE","siteName": "PRIVATE RESIDENCE","riskLevel": "2","street": "PRIVATE RESIDENCE","city": "SAN JOSE","state": "CA","ZIP": "95113","siteids": "CALUSTCA-T0608590822"},
                    { "id": "143147","lat": "37.36623","lng": "-121.86745","type": "1","listTypes": "CSL","sitenames": "San Jose Transit Village","siteName": "San Jose Transit Village","riskLevel": "1","street": "Northeast corner of North King Road and Dobbin Drive","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CAENSTOR-60000785"},
                    { "id": "142812","lat": "37.36412","lng": "-121.86951","type": "4~8","listTypes": "ERNS~GENERATOR~HAZMAT","sitenames": "CLEAN HARBORS SAN JOSE LLC~INTRA FAB INC~KEENE PRODS INC SAN JOSE DIV","siteName": "CLEAN HARBORS SAN JOSE LLC","riskLevel": "4","street": "660 LENFEST RD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALWDS-2 43I017732~CARIMSCA-99-4017~CASWIMCA-2 43I017732~NAHMIR08-E-2008110076~NAHMIR08-I-2008070076~NAHMIR09-E-2009060248~NAHMIR10-E-2010020071~NAHMIR10-E-2010100411~NAHMIR10-E-2010110442~NARCRA00-CAD980815997~NARCRA00-CAT080014459"},
                    { "id": "142772","lat": "37.36381","lng": "-121.86745","type": "4~8","listTypes": "ERNS~HAZMAT","sitenames": "Frank Lin Distillers Pro~FRANKLIN DISTILLERS~Rail Road","siteName": "Frank Lin Distillers Pro","riskLevel": "4","street": "625 NORTH KING ROAD","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CARIMS02-02-6220~CASAJOSE-1083~NAERNS90-01-564697"},
                    { "id": "142709","lat": "37.36329","lng": "-121.86885","type": "2","listTypes": "LUST","sitenames": "Carriage House Foods","siteName": "Carriage House Foods","riskLevel": "2","street": "665 Lenfest Rd","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608500313"},
                    { "id": "142668","lat": "37.36296","lng": "-121.86829","type": "1","listTypes": "CSL","sitenames": "ECOLAB INC","siteName": "ECOLAB INC","riskLevel": "1","street": "640 LENFEST RD","city": "SAN JOSE","state": "CA","ZIP": "95156","siteids": "CACSLLIS-T0608591790"},
                    { "id": "142550","lat": "37.36215","lng": "-121.86750","type": "1","listTypes": "CSL","sitenames": "ECOLAB INC","siteName": "ECOLAB INC","riskLevel": "1","street": "640 LENFEST AVE","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACSLLIS-T0608591623"},
                    { "id": "142552","lat": "37.36217","lng": "-121.86754","type": "2~4~8","listTypes": "CERCLIS~ERNS~GENERATOR~HAZMAT","sitenames": "Ecolab Inc~ECOLAB INC~ECOLAB INC.~ECONOMICS LAB INC","siteName": "Ecolab Inc","riskLevel": "2","street": "640 LENFEST ROAD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALWDS-2 43I002662~CARIMS04-04-6135~CARIMSCA-1995-8054~CASAJOSE-1161~CASWIMCA-2 43I002662~NACERNFA-0901192~NARCRA00-CAD009173246"},
                    { "id": "142436","lat": "37.36123","lng": "-121.86903","type": "2","listTypes": "LUST","sitenames": "International Paper","siteName": "International Paper","riskLevel": "2","street": "1601 Las Plumas Pl","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608502356"},
                    { "id": "142397","lat": "37.36098","lng": "-121.86736","type": "8","listTypes": "ERNS","sitenames": "Unknown","siteName": "Unknown","riskLevel": "8","street": "Los Plumas Ave. between Lenfest & King Rd.  near Ecco Labs 640 Lenfest","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CARIMS04-04-5972"},
                    { "id": "142398","lat": "37.36098","lng": "-121.86925","type": "2~4","listTypes": "HAZMAT~LUST","sitenames": "International Paper~Therma","siteName": "International Paper","riskLevel": "2","street": "1601 Las Plumas Ave","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASAJOSE-1151~CASCVWD1-07S1E04C01"},
                    { "id": "142407","lat": "37.36102","lng": "-121.86829","type": "2","listTypes": "LUST","sitenames": "International Paper","siteName": "International Paper","riskLevel": "2","street": "1601 Las Plumas Ave","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608500755"},
                    { "id": "143270","lat": "37.36716","lng": "-121.87045","type": "1","listTypes": "CSL","sitenames": "CHERRY ACRES PARTNERSHIP","siteName": "CHERRY ACRES PARTNERSHIP","riskLevel": "1","street": "1671 MABURY","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CAENSTOR-43330031"},
                    { "id": "143216","lat": "37.36666","lng": "-121.87006","type": "4~8","listTypes": "ERNS~GENERATOR~HAZMAT","sitenames": "EXION TECHNOLOGY INC~T A Technology Inc","siteName": "EXION TECHNOLOGY INC","riskLevel": "4","street": "1677 MABURY RD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CARIMSCA-97-2748~CASAJOSE-1283~NARCRA00-CAD981653900"},
                    { "id": "142980","lat": "37.36530","lng": "-121.87080","type": "2","listTypes": "LUST","sitenames": "Coors Distributor","siteName": "Coors Distributor","riskLevel": "2","street": "681 Lenfest Ave","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608501840"},
                    { "id": "142842","lat": "37.36433","lng": "-121.87063","type": "1","listTypes": "CSL","sitenames": "CLEAN HARBORS SAN JOSE, RAIL SPUR","siteName": "CLEAN HARBORS SAN JOSE, RAIL SPUR","riskLevel": "1","street": "660 LENFEST RD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CAPERCOR-CAL000191813"},
                    { "id": "142740","lat": "37.36357","lng": "-121.87065","type": "2~4","listTypes": "HAZMAT~LUST","sitenames": "Coors Distributor~Coors Distributors","siteName": "Coors Distributor","riskLevel": "2","street": "681 Lenfest Ave","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASAJOSE-1163~CASCVWD1-06S1E33P03"},
                    { "id": "142625","lat": "37.36268","lng": "-121.87056","type": "2","listTypes": "LUST","sitenames": "Butler Johnson Corp.","siteName": "Butler Johnson Corp.","riskLevel": "2","street": "1480 Nicora Ave","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608500279"},
                    { "id": "142538","lat": "37.36208","lng": "-121.87063","type": "2~4~8","listTypes": "ERNS~GENERATOR~LUST~WELLS","sitenames": "Carriage House Foods~CARRIAGE HOUSE FOODS~THE RED WING COMPANY, INC. - INACTIVE","siteName": "Carriage House Foods","riskLevel": "2","street": "665 LENFEST RD","city": "SAN JOSE","state": "CA","ZIP": "95150","siteids": "CASCVWD1-06S1E33P01~CAWWELLS-19555~NAERNS90-91-83661~NARCRA00-CAD981621550"},
                    { "id": "143179","lat": "37.36637","lng": "-121.87975","type": "2~4","listTypes": "HAZMAT~LUST","sitenames": "Harris Feeding Company~S J Tallow Co Inc~San Jose Tallow Co.~SRDC INC RECYCLING FACILITY","siteName": "Harris Feeding Company","riskLevel": "2","street": "11740 Berryessa Rd","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALWDS-2 43I017401~CASAJOSE-517~CASCVWD1-06S1E32J01~CASCVWD1-06S1E32J02~CASWIMCA-2 43I017401"},
                    { "id": "143111","lat": "37.36603","lng": "-121.87824","type": "2","listTypes": "LUST","sitenames": "Dext Feed","siteName": "Dext Feed","riskLevel": "2","street": "1255 Yard Ct","city": "SAN JOSE","state": "CA","ZIP": "95126","siteids": "CALUSTCA-T0608502355"},
                    { "id": "143124","lat": "37.36613","lng": "-121.87824","type": "2","listTypes": "LUST","sitenames": "Dext Feed","siteName": "Dext Feed","riskLevel": "2","street": "1255 Yard Ct","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASCVWD1-06S1E32J03~CASCVWD1-06S1E32J06"},
                    { "id": "143039","lat": "37.36560","lng": "-121.87278","type": "1","listTypes": "CSL","sitenames": "Adaptive Circuits, Div Of Viko Tech, Inc.","siteName": "Adaptive Circuits, Div Of Viko Tech, Inc.","riskLevel": "1","street": "1565-A Mabury Road","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CAENSTOR-71002920"},
                    { "id": "143051","lat": "37.36568","lng": "-121.87913","type": "2","listTypes": "LUST","sitenames": "Kunde Property","siteName": "Kunde Property","riskLevel": "2","street": "1259 Yard Ct","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASCVWD1-06S1E32J05"},
                    { "id": "143056","lat": "37.36574","lng": "-121.87295","type": "1~4~8","listTypes": "GENERATOR~HAZMAT~TSD","sitenames": "Adaptive Circuits~ADAPTIVE CIRCUITS~INFINITI CIRCUITS MFG, A DIV. OF INFINITI SOLUTIONS USA, INC.~U S M TECHNOLOGIES INC","siteName": "Adaptive Circuits","riskLevel": "1","street": "1565 #E MABURY ROAD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALWDS-2 43I015072~CASAJOSE-1280~CASWIMCA-2 43I015072~NARCRA00-CAD981692726~NARCRA00-CAD982498107"},
                    { "id": "142967","lat": "37.36523","lng": "-121.88220","type": "4~8","listTypes": "AST~HAZMAT","sitenames": "Norcal Waste System~NORCAL WASTE SYSTEMS OF SAN JOSE, INC~NORCAL WST SYSTEMS OF SAN JO","siteName": "Norcal Waste System","riskLevel": "4","street": "1120 Berryessa Rd","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALAST-6644~CACALWDS-2 43I017371~CASAJOSE-2333~CASWIMCA-2 43I017371"},
                    { "id": "142947","lat": "37.36515","lng": "-121.87998","type": "4~8","listTypes": "ERNS~HAZMAT","sitenames": "CA WST SOLUTIONS SAN~Calif Waste Solutions","siteName": "CA WST SOLUTIONS SAN","riskLevel": "4","street": "1005 Timothy Dr","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALWDS-2 43I017556~CARIMS03-03-4453~CASWIMCA-2 43I017556"},
                    { "id": "142892","lat": "37.36475","lng": "-121.88068","type": "4~8","listTypes": "ERNS~GENERATOR~HAZMAT","sitenames": "Elcon~ELCON INC~ELCON, INC","siteName": "Elcon","riskLevel": "4","street": "1009 TIMOTHY DR","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALWDS-2 43I013252~CASAJOSE-2173~CASWIMCA-2 43I013252~NAERNS08-878786~NARCRA00-CAD981399959"},
                    { "id": "142854","lat": "37.36443","lng": "-121.87147","type": "2~4~8","listTypes": "GENERATOR~HAZMAT~LUST","sitenames": "Kaye-Smith~KAYE SMITH BUSINESS GRAPHICS~Lenfest Associates","siteName": "Kaye-Smith","riskLevel": "2","street": "697 LENFEST RD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CASAJOSE-1164~CASCVWD1-06S1E33L01~NARCRA00-CAD983606070"},
                    { "id": "142785","lat": "37.36390","lng": "-121.87820","type": "2","listTypes": "LUST","sitenames": "Dext Feed~Kunde Property","siteName": "Dext Feed","riskLevel": "2","street": "1259 Yard Ct","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CALUSTCA-T0608500204~CALUSTCA-T0608501327"},
                    { "id": "142800","lat": "37.36404","lng": "-121.87862","type": "2~4","listTypes": "CERCLIS~HAZMAT~LUST","sitenames": "Amoroso Construction~BRUIN ELECTRONICS INC~Sanmina Corp & Plant 8","siteName": "Amoroso Construction","riskLevel": "2","street": "1015 TIMOTHY DR","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CASAJOSE-2175~CASCVWD1-06S1E32J04~NACERNFA-0902507"},
                    { "id": "142754","lat": "37.36368","lng": "-121.87245","type": "2","listTypes": "LUST","sitenames": "Graebel Erikson Movers","siteName": "Graebel Erikson Movers","riskLevel": "2","street": "1460 Mabury Rd","city": "SAN JOSE","state": "CA","ZIP": "","siteids": "CASCVWD1-06S1E33M01"},
                    { "id": "142721","lat": "37.36337","lng": "-121.88271","type": "2~4","listTypes": "HAZMAT~LUST","sitenames": "Clarklift~Moore's Material Handling~MOORE MATERIAL HANDLING GROUP","siteName": "Clarklift","riskLevel": "2","street": "875 MABURY RD","city": "SAN JOSE","state": "CA","ZIP": "95133","siteids": "CACALWDS-2 43I006590~CASAJOSE-1270~CASCVWD1-06S1E32Q01~CASWIMCA-2 43I006590"},
                ],
                    "totalCount": 57, 
                    "success": true 
                };


            Ext.grid.Panel.override({
                initComponent    : function(){
                    var me = this;
                    me.callParent();
                    me.on('scrollershow', function(scroller) {
                        if (scroller && scroller.scrollEl) {
                            scroller.clearManagedListeners(); 
                            scroller.mon(scroller.scrollEl, 'scroll', scroller.onElScroll, scroller); 
                        }
                    });
                }
            });
            
            Ext.define('Record', {
                extend: 'Ext.data.Model',
                fields: [
                        {name: "id", type: 'string'}, 
                        {name: "lat", type: 'float'}, 
                        {name: "lng", type: 'float'}, 
                        {name: "type", type: 'string'}, 
                        {name: "listTypes", type: 'string'}, 
                        {name: "siteName", type: 'string'}, 
                        {name: "riskLevel", type: 'string'}, 
                        {name: "street", type: 'string'}, 
                        {name: "city", type: 'string'}, 
                        {name: "state", type: 'string'}, 
                        {name: "ZIP", type: 'string'}, 
                        {name: "siteids", type: 'string'}
                ]
            });
            
            var gridStore = Ext.create('Ext.data.Store', {
                autoLoad: true,
                model: 'Record',
                data: sitesData,
                proxy: {
                    type: 'memory',
                    reader: {
                        type: 'json',
                        root: 'records',
                        totalProperty: 'totalCount'
                    }
                }
            });
            
            this.activeDetailsGrid = {
                xtype: 'grid',
                store: gridStore,
                selType: 'rowmodel',
                //autoScroll: false,
                scroll: true,
                id: 'grid-panel',
                columns: [
                      { id: 'subjectHit', header: "S", width: 25, sortable: true, dataIndex: 'subjectHit' },
                      { id: 'id', header: "Site ID", width: 50, sortable: true, dataIndex: 'id' },
                      { text: "Site Name", width: 150, sortable: true, dataIndex: 'siteName' },
                      { text: "Street", width: 150, sortable: true, dataIndex: 'street' },
                      { text: "City", width: 75, sortable: true, dataIndex: 'city' },
                      { text: "ST", width: 30, sortable: true, dataIndex: 'state' },
                      { text: "ZIP", width: 50, sortable: true, dataIndex: 'ZIP' },
                      { text: "Risk", width: 50, sortable: true, dataIndex: 'riskLevel'},
                      { text: "Site Types", width: 125, sortable: true, dataIndex: 'listTypes' },
                ]
            };
    
          var viewport = Ext.create('Ext.Viewport', {
              id: 'border-example',
              layout: 'border',
              split: true,
              items: [{
                      xtype: 'panel',
                      layout: 'border',
                      region: 'east',
                      split: true,
                      width: 300,
                      items: [{
                          title: 'Site Details',
                          xtype: 'panel',
                          height: 150,
                          region: 'center',
                          margins: '0 5 0 0',
                          items: this.activeDetailsGrid
                      }, {                
                          xtype: 'tabpanel',
                          title: 'Search/Filter Actions',
                          collapsible: false,
                          region: 'south',
                          split: true,
                          height: 200,
                          margins: '0 5 0 0',
                          activeTab: 1,
                          tabPosition: 'bottom',
                          items: [{
                                title: 'Search',
                                autoScroll: true
                          }, {
                              title: 'Filter',
                              id: 'filter-panel',
                              autoScroll: true,
                              bodyPadding: 5
                                                        
                          }]
                        }]
                    }, {
                        xtype: 'panel',
                        id: 'map-panel',
                        region: 'center', // a center region is ALWAYS required for border layout
                        html: 'Map Goes Here',
                        tbar: toolbar
                  }]
            });


        });


    </script>


</head>
<body>
    <div id="Main">
    
    </div>


</body>
</html>