Dynamically changing the tree data produces undesired effects - items and scrollbar disappear

Found in the latest Flex 3 beta.

If the data changes after the tree item is expanded, the tree is not properly updated to reflect this. For example, I call a HTTPService / RemoteObject which returns new nodes for the item I just expanded. There is potentially no data in the tree node when it is being expanded. After updating the data, I get undesired results, including render errors.

Steps to reproduce:
1. Run attached source
2. Expand/Collapse various items in the tree
3. scroll (if scrollbar is present)

Actual Results:
Items disappear, or actually change as you scroll up/down
entire branches disappear, and the sub nodes appear in other branches.

Expected Results:
The scrollbar should be present when the data is changed in such a way that more items are visible.
Tree nodes should not disappear.

Workaround (if any):

I have not found one yet. although I have tried many. Including this, which I thought worked at first, but does not.

myTree.expandItem(expandedNode,true);
myTree.expandItem(expandedNode,false);
myTree.validateNow();
myTree.expandItem(expandedNode,true);
myTree.expandItem(expandedNode,false);
myTree.expandItem(expandedNode,true);
myTree.validateNow();