title: Extjs ComboBox doesn't pick the correct value when setValue is called
body: <p>I have the following code:</p>
  
  <pre><code>// Part of a larger form.
  {
      xtype: 'combo',
      id: 'enroller',
      valueNotFoundText: 'not found',
      triggerAction: 'all',
      mode: 'local',
      fieldLabel: 'Enroller',
      store: new Ext.data.JsonStore({
          url: url,
          root: 'data',
          autoLoad: true,
          fields: ['enrollerID', 'name', 'key']
      }),
      displayField: 'name',
      valueField: 'key',
      hiddenName: 'enrollerID',
      forceSelection: true
  }
  // Other area of code.
  Ext.getCmp('enroller').setValue(289);
  </code></pre>
  
  <p>Even though I can confirm the store has a record that looks like:</p>
  
  <pre><code>{"name":"Test Enroller","enrollerID":"289","key":"289"}
  </code></pre>
  
  <p>The combo box displays the valueNotFoundText. How can I get the combo to load the correct record?</p>