After Logout On 2011 15" MBP, Display Resolution Drops, And Can't Be Changed Without A System Restart.

So I bought a 2011 15" Macbook Pro in March, 2.0 GHz Intel Quad-Core i7, 4GB RAM, OS X 10.6.8, And every few days when I log out of my account, the resolution on the internal display has somehow been changed to a much lower resolution, and if I log back in the change this in display settings, it thinks the resolution is still at the maximum, 1440x900, and there is no way to change it back. The only way I have found to work is by restarting the computer, and it's back to normal. Is there anything I can do about this?!