losing gamma settings when play DoD (HL mod)

When I go to play DoD my gamma reverts to the normal non adjusted gamma setting. After I have quit the game I then have to go to the settings and "re-apply" the gamma. The number is set at 1.35 and does not change, I just have to reselect it and then the gamma increases again. I have done this in game and soon as I go back to the game the gamma decreases again Any help?

I have an Asus 9600 XT, Cat 3.9s, and XP SP1.