To reproduce, run the JavaFX 2 application in the attached NetBeans project and do the following:
1. Expand the 'A' node. The vertical and horizontal scroll bars will appear.
2. Scroll down as far as you can go using the vertical scroll bar.
3. Expand the 'B' node.
You will notice that the 'E' node is hidden beneath the horizontal scroll bar and it is not possible to make it appear by clicking the down arrow of the vertical scroll bar.
You can make the 'E' node appear by first scrolling up and then scrolling down again either by using the vertical scroll bar or the mouse wheel.
Another workaround is to make the children elements narrower so the horizontal scroll bar does not appear, but this is not always practical