This problem still occurs with Xorg 7.1. It is caused by XF86DGAGetVideo() programming XF86Cleanup() as a atexit() callback while XF86Cleanup() calls _exit(). The code is dirty, but it is possible to fix it. I have reported and posted a patch upstream at https://bugs.freedesktop.org/show_bug.cgi?id=9815. Brice