title: Extjs4, How to set displayField in combo editor?
body: <p>In combo editor, after select a option, it display value even I set display Field.
  Once I click the combo editor, it will display displayField as well, but after select and click the others (It means mouse out) then the cell value changed to valueField.</p>
  
  <p>my combo editor code,</p>
  
  <pre><code>{
     xtype : 'combo',
     editable : false,
     triggerAction : 'all',
     displayField : 'name',
     valueField : 'id',
     store : myStore
  }
  </code></pre>
  
  <p>what I missed?</p>
  
  <p>anyone know, please advice me~</p>
  
  <p>Thanks!</p>
  
  <p>[Edit]</p>
  
  <p>I write test code in here : </p>
  
  <p><a href="http://jsfiddle.net/ilovekanon/NQXw9/" rel="nofollow">http://jsfiddle.net/ilovekanon/NQXw9/</a></p>
  
  <p>change name and click the others then the name will show ID, not name :(</p>