Gamma issue when running the game

[Wacher]

(iMac 2009 - Core 2 duo - 3.06 Gh - OS X 10.6.8 - 64 bits)

I play amnesia on high settings and it works fine, I have no problems.
The other day I was playing a custom story and the game was very very dark. I checked the settings to see if the gamma was set to 1.0 again. It wasn't. It was at 1.3 but the screen was like if it was set at 1.0 and when I pressed cancel the screen got brighter as if it actually run with 1.3 gamma.

Later on that same day I opened amnesia and once again the gamma was at 1.0 but in the settings it said it was at 1.3, I pressed cancel and the screen changed to it's actual gamma setting.
I tried to restart my mac to see if it was a RAM problem and when I run the game the gamma was ok. But once again (this is getting very repetitive), later on I started the game and the gamma wasn't working properly.

If I open the settings and press cancel or turn up and down the gamma it works fine but is a bit annoying to do it over and over again.

Any idea of how to solve the issue?
PS: I have the latest patch.