title: Extjs combobox autocomplete doesn't work
body: <p>I have an editor grid and a combobox is one of its fields.
  The combobox uses a json store.
  Here is the combobox code:</p>
  
  <pre><code>var patternCmb = new Ext.form.ComboBox({ //combobox for workers
      store:  dsPatterns,
      valueField: 'pid',
      displayField: 'pname',
      typeAhead:true, 
      lazyRender:true,
      forceSelection:true,
      minChars: 2, 
      valueNotFoundText:"not found",
      editable: true,
      triggerAction: 'all' 
  });
  </code></pre>
  
  <p>After typing the third character the FIRST (not correct) value of the store is selected. What can be the problem?</p>