We have been using version 4.1.1 and are migrating to 4.2.0.663. We have editor grids with buffered stores which contain large volume of data. The editor grids are similar to the row-editing example(except that it uses buffered store). But the add functionality for the grid has stopped after migration and it raises an error
Ext.Error: insert operation not supported into buffered Store.

HTML Code:
var rowEditing = Ext.create('Ext.grid.plugin.RowEditing', {
        clicksToMoveEditor: 1,
        autoCancel: false
    });

    // create the grid and specify what field you want
    // to use for the editor at each column.
    var grid = Ext.create('Ext.grid.Panel', {
        store: store,
        columns: [{
            header: 'Name',
            dataIndex: 'name',
            flex: 1,
            editor: {
                // defaults to textfield if no xtype is supplied
                allowBlank: false
            }
        }, {
            header: 'Email',
            dataIndex: 'email',
            width: 160,
            editor: {
                allowBlank: false,
                vtype: 'email'
            }
        }, {
            xtype: 'datecolumn',
            header: 'Start Date',
            dataIndex: 'start',
            width: 90,
            editor: {
                xtype: 'datefield',
                allowBlank: false,
                format: 'm/d/Y',
                minValue: '01/01/2006',
                minText: 'Cannot have a start date before the company existed!',
                maxValue: Ext.Date.format(new Date(), 'm/d/Y')
            }
        }, {
            xtype: 'numbercolumn',
            header: 'Salary',
            dataIndex: 'salary',
            format: '$0,0',
            width: 90,
            editor: {
                xtype: 'numberfield',
                allowBlank: false,
                minValue: 1,
                maxValue: 150000
            }
        }, {
            xtype: 'checkcolumn',
            header: 'Active?',
            dataIndex: 'active',
            width: 60,
            editor: {
                xtype: 'checkbox',
                cls: 'x-grid-checkheader-editor'
            }
        }],
        renderTo: 'editor-grid',
        width: 600,
        height: 400,
        title: 'Employee Salaries',
        frame: true,
        tbar: [{
            text: 'Add Employee',
            iconCls: 'employee-add',
            handler : function() {
                rowEditing.cancelEdit();

                // Create a model instance
                var r = Ext.create('Employee', {
                    name: 'New Guy',
                    email: 'new@sencha-test.com',
                    start: Ext.Date.clearTime(new Date()),
                    salary: 50000,
                    active: true
                });

                store.insert(0, r);
                rowEditing.startEdit(0, 0);
            }
        }],
        plugins: [rowEditing],
});
Please advise on what is the approach to be followed.