Crossfire at SIMO

[MatiasZ]

Yesterday I was at the SIMO, a technology fair in Madrid (where lots of different vendors reunite and show off stuff, as in E3 but much more business oriented). At the ASUS stand, they were showing off a system running an X800 Crossfire setup, running Quake 4. I don't have much more info on how this was setup, all I know is that it was an Asus Motherboard with an ATI chipset (RS480?), and to X800 cards.
Looking at the screen, I could notice a CLEAR difference in 'brightness' between the upper half on the screen, and the half on the bottom. There was a 'line' dividing the two, caused by the different in brightness, or gamma, or something on the image.

This was REALLY noticeable, and I haven't seen it posted anywhere else, so I don't know if this can be a case of their setup (maybe the cables running the setup being of bad or different quality?) or something that is supposed to happen with this kind of setups. Has anybody seen / heard about this before?

 

[wireframe]

Maybe they set the brightness/gamma differently for the two cards or some demo mode to draw your eyes to the fact that two cards are rendering at the same time.

 

[MatiasZ]

I was talking to the guy who set it up, and he said he had no idea why it was happening. He even said he thought it was 'normal'. Is it possible to set the gamma - brightness contrast or whatever different for the two cards under Crossfire?