Tree display not updating when adding first node to expanded node

Question

Hi
Please have a look at the following code. To reproduce the faulty behaviour you have to expand the item, then click "add" button and observe, that nothing happens. Collapsing, then expanding the node shows the added children. I use Flex 3.5.0
Is this a bug in the SDK or am I missing some auto update switch?
Thanks!!
<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" layout="horizontal"
     minWidth="955" minHeight="600"
     creationComplete="run()">
     <mx:Tree id="tree" width="300" height="500" labelField="name" />
     <mx:Button label="add" click="onClickAdd()" />
     <mx:Script>
          <![CDATA[
               import mx.collections.ArrayCollection;
               import mx.utils.ObjectProxy;
               protected var itm1:Object;
               protected function run() : void
                    var ac:ArrayCollection = new ArrayCollection();
                    this.itm1 = new ObjectProxy({name:"1", children:new ArrayCollection()});
                    ac.addItem(this.itm1);
                    this.tree.dataProvider = ac;
               protected function onClickAdd() : void
                    this.itm1.children.addItem({name:"child"});
          ]]>
     </mx:Script>
</mx:Application>

Answer 1

Yep, that works! Thanks! Would have never thought of that...
Here is my modified code:
          <mx:Tree id="tree" width="300" height="500" labelField="name"
          dataDescriptor="{new DefaultDataDescriptor2()}"
          />
and new class
package de.byteconsult.controls.tree
     import mx.collections.ICollectionView;
     import mx.controls.treeClasses.DefaultDataDescriptor;
     public class DefaultDataDescriptor2 extends DefaultDataDescriptor
          public function DefaultDataDescriptor2()
               super();
          override public function hasChildren(node:Object, model:Object=null) : Boolean
               var children:ICollectionView = this.getChildren(node, model);
               return children != null;