Philips 42" Plasma - Brightness Changes By Itself?

I purchased a Philips 42PFP5332D/37 42" plasma from Newegg in early April. Now, I'd be extremely happy with the TV, except my brightness and color values always decrease, at a random rate (sometimes 1-2 points per minute, sometimes 1-2 points per hour).

I wanted to know if anyone else is aware of this kind of a problem and whether there exists a known solution.

Thanks in advance.

P.S. I am using HDMI with a 720p signal coming from my cable box.

No, I do not. I've tried playing with every configuration option, and have even upgraded the firmware. Still, the problems remain unabated.

I have done that. It drops to about 20 for brightness and 10 for color... but never actually stops at a round number. I've never run the TV for more than 4-5 hours continuously, but if I don't adjust the settings for a few days, I usually find them in the 20s.

I was running something that was 0.9b, and upgraded to 1.1

Unfortunately the problem still persists.

Thanks for your help and attention by the way.