Well the symptoms are present since well before the 4191 drivers for me.
The workaround I found is that whenever I log out, I restart the X server before login in again. If I don't do this, video players make X crash (or Quake can cause the whole system to crash, which seems to be a very serious situation -- only a SysRq B can reboot the machine).
But it doesn't seem to be the same bug as you. Mine is more like this