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HTML

<link rel="stylesheet" href="http://dev.sencha.com/deploy/ext-4.0.2a/resources/css/ext-all.css">
<html>
    <head>
        <title>ExtJS4 Button-Menu-Combo Focus Bug</title>
    </head>
    <body>
    </body>
</html>

JavaScript

// ExtJS 4 Button-Menu-Combo Focus Bug                                         
//**************************//                        

Ext.onReady(function(){
    
    Ext.create('Ext.Window',{
        title: 'ExtJS 4 Button-Menu-Combo Focus Bug'
        , width: 300
        , height: 200
        , items: [{
            xtype: 'button',
            text: 'Show Menu /w Combo',
            menu: {
                xtype : 'menu'
                plain: true,
                items: [
                    {
                        xtype: 'combo',
                        width: 300,
                        queryMode: 'local',
                        typeAhead: true,
                        forceSelection: true,
                        minChars: 1,
                        displayField: 'name',
                        valueField: 'abbr',
                        store: Ext.create('Ext.data.Store', {
                            fields: ['abbr','name'],
                            data: [
                                {"abbr":"AL", "name":"Alabama"},
                                {"abbr":"AK", "name":"Alaska"},
                                {"abbr":"AZ", "name":"Arizona"}
                            ]
                        })
                    },
                    {
                        xtype: 'button',
                        text: 'Process'
                    }
                ]
            }
        }]
    }).show();
});