AC ignores system brightness setting

[Boomhauer]

Whenever I leave the game, "Alt + Tab" to return the brightness decreases. So I need to use / gamma ...
The number I use does not work again, example:
If I use / gamma 185 and get out of the game "Alt + Tab", the back is dark again. And if i put again / gamma 185, nothing happens. I need to use another number, such as / gamma 186, or others.

Same.. on Windows 7 computer anyway.