I've noticed the bug since XFree-4.1 is in woody. using the ati-module from the XFree-4.0 packages worked it out for some time, but after the last XFree-uptate it became even worse with the last X-Server update. So I've tracked it down to the WMCPU applet as I reported. And: no, it doesn't need a WindowMaker to be running to crash the server, but it might need some libs (the libdockap afaik)
Willi