title: ExtJs ComboBox reinitializing
body: <p>I'm trying to change ComboBox configuration by reinitializing:</p>
  
  <pre><code>Ext.onReady(function(){
  
     var mycb = new Ext.form.ComboBox({
         //params
     });
  
     //here is other component initizing
     var other = ....
        onChange: function() {
          //here I'm trying to reinitialize ComboBox
          mycb = new Ext.form.ComboBox({
             // other params
          });
     }
  });
  </code></pre>
  
  <p>But after onChange event my ComboBox's disapeared. I tried to invoke mycb.destroy() methods, but there's the same result.</p>
  
  <p>Should I unregister or something like that ComboBox? Why my component is disapearing?</p>