XFree86 hangs machine on exit

[Johannes.Hofmann at gmx.de]

XFree86 with the siliconmotion driver does not restore the console properly
on exit and hangs the machine (no kernel debugger or anything).
This is not a new problem. It also existed on FreeBSD, and a similar problem
is reported to XFree86 as bug #124 http://bugs.xfree86.org/show_bug.cgi?id=124 

But with prior DragonFly kernels the problem happend only about every 10th 
time shutting down X. Now (cvs of Wed Jun  9 23:15:53) it seems to 
happen always.

Any ideas on how to track this down?

Best regards,
Johannes