Delete is broken in Hierarchical Data

I have a AdvancedDataGrid where I am deleting the children. When all the children are gone the folder icon does not change. If I walk the collection and then force the children = null, then the folder changes to a sheet (leaf) icon, as you would expect by looking at the HierachicalCollection class. However when I go to add a new leaf to the summary folder the folder reappears and the down arrow opens indicating that it's got a child, but the child does not render.

Repro using this is swf.

<?xml version="1.0" encoding="utf-8"?>
<mx:Application layout="horizontal"
viewSourceURL="srcview/index.html"
xmlns:mx="http://www.adobe.com/2006/mxml%22>
<mx:Script>
<![CDATA[
import mx.collections.ArrayCollection;
import mx.collections.IHierarchicalCollectionView;
import mx.collections.ICollectionView;
import mx.collections.HierarchicalData;
[Bindable] public var tasks:HierarchicalData = new HierarchicalData([{id: "T1", name: "Task #1", startTime: "1/14/2008 8:0:0", endTime: "1/28/2008 17:0:0"}, {id: "T2", name: "Task #2", startTime: "1/29/2008 8:0:0", endTime: "2/5/2008 17:0:0"},
{id: "T3", name: "Summary Task #1", startTime: "2/5/2008 8:0:0", endTime: "2/17/2008 17:0:0", children: [{id: "T4", name: "Task #3", startTime: "2/5/2008 8:0:0", endTime: "2/12/2008 17:0:0"},
{id: "T5", name: "Task #4", startTime: "2/13/2008 8:0:0", endTime: "2/17/2008 17:0:0"}]},
{id: "T6", name: "Milestone #1", milestone: "true", startTime: "2/17/2008 17:0:0", endTime: "2/17/2008 17:0:0"}]);

private function onDelete():void {
var task:Object = adGrid.selectedItem;
if(task != null) {
var _taskCollection:IHierarchicalCollectionView = IHierarchicalCollectionView(adGrid.dataProvider);
var parentTask:Object = _taskCollection.getParentItem(task);
_taskCollection.removeChild(parentTask, task);
//trace(parentTask.id + " has children = " + tasks.hasChildren(parentTask));
//this.cleanTaskCollection(tasks.source as Array);
_taskCollection.itemUpdated(parentTask);
//_taskCollection.refresh();
} else {
mx.controls.Alert.show("Please select a node");
}
}

private function cleanTaskCollection(collection:Array):void {
for each(var task:Object in collection) {
if(task.children && task.children.length == 0) {
// attempt to force item render to not show folders
task.children = null;
} else {
// recurse
cleanTaskCollection(task.children);
}
}
}
private var count:int = 0;

private function onAdd():void {
var task:Object = adGrid.selectedItem;
if(task != null) {
var child:Object = new Object;
child.id = count++;
child.name = "new node " + count;
if(task.children == null) {
task.children = new Array();
}
var _taskCollection:IHierarchicalCollectionView = IHierarchicalCollectionView(adGrid.dataProvider);
_taskCollection.addChild(task, child);
} else {
mx.controls.Alert.show("Please select a node");
}
}
]]>
</mx:Script>
<mx:AdvancedDataGrid dataProvider="{tasks}"
designViewDataType="tree"
id="adGrid">
</mx:AdvancedDataGrid>
<mx:Button click="onDelete()"
label="delete">
</mx:Button>
<mx:Button click="onAdd()"
label="add">
</mx:Button>
</mx:Application>