(I know its old)
AFAIK XGL hates other 3D apps. If you dont need it, you can disable it.
mkdir -p ~/.config/xserver-xgl
touch ~/.config/xserver-xgl/disable
After logging out and in again, XGL should be disabled. To enable it again:
rm ~/.config/xserver-xgl/disable
At the time I needed it for Compiz Fusion. It doesn't matter anymore because of the new ATI drivers (And my new card).