openGL cannot do fullscreen in dual monitor config

[Erik Steffl <steffl@bigfoot.com>]

  just tried dual monitors with two card (geForce FX 5600 Ultra, nvidia 
drivers and ATI Radeon 9800, ati drivers), debian unstable, X 4.2.1:

  one monitor: openGL works fullscreen or windowed

  two monitors: openGL works in window, not fullscreen

  tested with xscreensaver hacks

  considering that these are two fairly different implementations of 
openGL (I think, they both provide openGL libs and their own way to set 
up two monitors) - is there something that I should set up to be able to 
run fullscreen openGL apps fullscreen? or is some way to set up dual 
monitors better than other when using fullscreen openGL apps?

  TIA

	erik