title: Unable to select from combobox after adding empty item/row
body: <p>I implemented as said at  <a href="https://stackoverflow.com/questions/9399771/how-to-add-an-empty-item-to-extjs-combobox/14989155">How to add an empty item to ExtJS combobox?</a> I can see a blank row/item as desired but I am <strong><em>unable</em></strong> to select any of the item from combobox !</p>
  
  <p>Any guess ?</p>
  
  <p>My code is as follow</p>
  
  <pre><code>var rModel = Ext.regModel('State', {
    fields: [
       {type: 'string', name: 'fips_state_code'},
       {type: 'string', name: 'state_name'}
    ]
  });
  
  // The data store holding the states
  
  var store = Ext.create('Ext.data.Store', {
    model: 'State',
    data: [{fips_state_code: '0', state_name: ' '}]
  });
  
  store.add(obj.results);
  
  {
        xtype:'combo',
        id:'filterstate',
        width: 250,
        fieldLabel: 'Filter By State',
        store: store,
        queryMode: 'local',
        displayField: 'state_name',
        valueField: 'fips_state_code',
        editable: false,
        forceSelection : true,
        triggerAction : 'all',
        typeAhead: true,
        selectOnFocus:true,
        allowBlank:true,
        tpl : '&lt;tpl for=\".\"&gt;&lt;div class=\"x-combo-list-item\"&gt;{state_name}&amp;nbsp;&lt;\/div&gt;&lt;\/tpl&gt;'
  
      }
  </code></pre>