TreeView scrollbar's thumb should not be seen, if Root node is collapsed.

Build used is javafx-sdk2.0-ea
Windows XP SP3 and Vista

Step to reproduce :-
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1) Run the Ensemble.jar application.
2) Select TreeView control from controls node of the tree.
3) Click on the Treeview, so that treeview gets the focus.
4) Click on the "child node3" , so the Child node3 gets expanded and you will see the scrollbar.
5) Navigate to the last node and then move the selection towards the Root Node using keyboard and collapse the root node. i,e press right arrow key on the root node.

Observe that TreeView Scrollbar thumb is seen and its small.
Expected Result :- When root node is collapsed , treeview scrollbar should not be seen.
Actual Result :- When root node is collapsed , treeview scrollbar and thumb is seen.

I have attached the screen shot.