Jeff Sparkes writes:

 > It appears that the toolbar is being cleared and recreated for every
 > redraw.

Note to Windows users:

I suspect this was Windows-related, or at least done by a Windows
coder.  There are many places where subwindows are dirtied explicitly,
which is way inefficient in Xt or GTK+ coding.  At least from the
XEmacs code I've looked at, it doesn't seem like Windows has a proper
notion of "widget", so you need to redraw stuff "by hand" all the
time.