3D shape not clipped by ScrollPane properly?

[Mike Hearn]

I have a ScrollPane into which I put a Pane with a min width/height, and
then I place a Button and a Sphere. For both of them I use setLayoutX/Y to
move them around.

Now when I scroll the ScrollPane I can see it move the button around
correctly, and the sphere, but the sphere is able to draw over the
scrollbars. It's not being clipped like the Button is.

I have not configured any special cameras or the like.

Do 3D objects clip differently to 2D objects? If so, why?