opengl visibility strange

[flokno]

hello!

i have a matrox g550 video card with two heads but presently not running xinerama.

when using xinerama:
x segfaults when i test any open/gl screensaver. how can i fix this problem?

when not using xinerama:
opengl works but has strange problems with visibility.
the gears in xscreensaver seem to be seen from behind but are drawn from front to back (i see the inside of the gears). same problem with cage (seems like a drawing done by Escher).

things work on the second unaccelerated head of my matrox.

these strange problems occur on my second computer with my nvidia too.

any help is very welcome.

-- flo