Broken RowEditor in ExtJS 4.2.1

1.) Add a new record. 2.) Car is required 3.) Even after entering a value, "Update" button isn't enabled and error summary isn't dismissed

by existdissolve

HTML

<link rel="stylesheet" href="http://cdn.sencha.com/ext/gpl/4.2.1/resources/css/ext-all.css">
<script src="http://cdn.sencha.com/ext/gpl/4.2.1/ext-all.js"></script>

JavaScript

Ext.create('Ext.grid.Panel',{
    frame: true,
    store: Ext.create('Ext.data.Store',{
        fields: ['car','driver'],
        data: [
            {car:'Ford',driver:'Joel'},
            {car:'Chevy',driver:'Tom'},
            {car:'Dolorian',driver:'Joel'}                       
        ]       
    }),
    plugins: Ext.create('Ext.grid.plugin.RowEditing', {
        clicksToEdit: 2
    }),
    columns: [
        {
            text: 'Car',
            dataIndex:'car',
            editor: {
                xtype: 'textfield',
                allowBlank: false
            }
        },
        {
            text: 'Driver',
            flex: 1,
            dataIndex:'driver',
            editor: {
                xtype: 'combobox',
                queryMode:'local',
                displayField:'label',
                valueField:'value',
                store: Ext.create('Ext.data.Store',{
                    fields: ['label','value'],
                    data: [
                        {label:'Joel',value:'Joel'},
                        {label:'Tom',value:'Tom'},
                        {label:'Sara',value:'Sara'}                       
                    ]
                })                    
            }
        }
    ],
    dockedItems: [
        {
            xtype: 'toolbar',
            items: [
                {
                    xtype: 'button',
                    text:'Add',
                    handler: function(btn) {
                        var grid = btn.up( 'grid' ),
                            store=grid.getStore()
                        store.insert( 0, {} );
                    }
                }
            ]        
        }                            
    ],
    renderTo:Ext.getBody()    
});