Unnecessary Display Refreshing Hurts Performance?

I noticed that the Earth example in visad/examples continues to use up
processor time even when the cursor is outside both of its windows.  On
my Sun Ultra 60 I see this by repeatedly doing "ps -ef | grep java" and
looking at the accumulated time.

Actually, I first noticed this on my real application, which gets slower
as I add more displayed data.  It eventually gets to the point where it
takes 20 seconds to refresh a window with nothing but a JTable in it.  I
have another Java3D program which doesn't use VisAD, and it doesn't have
this behavior.

Profiling suggests a lot of time spent in the J3D-Renderer-1 thread in
Canvas3D.callDisplayList.  My question is, is VisAD continually
refreshing the display even when it hasn't changed?  If so, why, and how
can I make it stop?  Or have I misunderstood what's going on?

Thanks for any help.

Randall W. Simons
Sandia National Laboratories