title: Why does a node in a TreePanel not show a load icon after I replaced the default icons?
body: <p>I replaced the default icons of tree-nodes in my TreeStore:</p>
  
  <pre><code>  listeners: {
       append: function( oParentNode, oAppendedNode ) {
          oAppendedNode.set( 'icon', Ext.BLANK_IMAGE_URL );
       }
    }
  </code></pre>
  
  <p>But now they don't show the loading icon anymore.
  Is there any simple way to get it back?</p>