Bug#216933: Another datapoint...
I also see the annoying BadLength/X_ChangeProperty on my p2120/ATI
Radeom M6/XFree86 4.3.0 (Fedora). I've experimented a little, and at one
point I had two displays running simultaneously, one showing the problem
and the other not. This was with two different executables, the standard
one and an executable made with "makeg" (link step only).