I bought a 50" Samsung plasma TV from Conn's for $599 about 6 months ago and it just recently started doing the same thing, automatically switching from the standard picture mode to the bright dynamic mode. Definitely annoying. Is this an error or is it programmed to choose the optimum picture setting? It's weird because it just started doing this about two weeks ago. I'm pretty happy with it otherwise....
The problem that was referred to doesn't have to do with the picture settings being toggled without warning, its an anomaly known as "flicker" that exists in a few runs of Samsung plasmas. You can fix it by having the logic board replaced, free if its still under the manufacturers warranty. You may or may not have flicker, I can't really tell. Go research it.
