I've got a very simple viewport that I created to use in a shared development environment where we're ramping up on extjs... For the moment it's just a toolbar and a tab panel. Using extjs 4.0.7 this renders as expected (3 tabs, with the inlined html), works fine in both IE7 and Firefox. When I updated to the 4.1.0-beta2 it stopped working in IE7, now I only get the toolbar and nothing of the tab panel. Firefox still renders it just fine. My app.js is basically empty other than the autoCreateViewport:true ...

Code:
Ext.define('lwdiag.view.Viewport', {
    extend: 'Ext.container.Viewport',

    layout: 'fit',

    requires: ['Ext.tab.*'],

    initComponent: function() {
    this.items = {
        dockedItems: [{
            dock: 'top',
            xtype: 'toolbar',
            height: 20,
            items: [{
                xtype: 'component',
                html: 'navigation toolbar'
            }]
        }
        ],
        layout: {
            type: 'border'
        },
        items: [{
            width: 600,
            xtype: 'tabpanel',
            activeTab: 0,
            region: 'center',
            items: [{
                xtype: 'panel',
                title: 'Content Panel 0',
                html: '<center>Panel Content</center>'
            },
            {
                xtype: 'panel',
                title: 'Content Panel 1',
                html: 'For testing purposes replace this entry with "xtype:<yourviewalias>" and remove the html entry'
            },
            {
                xtype: 'panel',
                title: 'Content Panel 2',
                html: 'For testing purposes replace this entry with "xtype:<yourviewalias>" and remove the html entry'
            }]
        }]
    }

    this.callParent();
    }

});
Did something change in 4.1 related to default height maybe? There are no errors in firebug or in IE...

Thanks!