sounds like what they call flashlighting. i had the same issue with a samsung set i bought several years ago. they worked with me well and sent replacements, but they never sent me one that completely got rid of it. the third one they sent finally only had a very little bit in one corner. it was acceptible but not perfect. no panel is perfect. but some are damn close. it was a real hassle, and to be honest i thought they had solved this problem. you may have just gotten a rare bum one. call them immediately. and now that you bring this up, i was just about to pull the trigger on a ks8000 but you have me second guessing it. i don't want to go through that again.
edit: and the only reason i kept the one with minimal flashlighting was because you really couldn't notice it when i played games in game mode. otherwise it was annoying but eventually i just kind of stopped noticing it. now the same tv has a large wavy line/discoloration that looks like a water spot (it's very old now) so it's driving me nuts and i'm champing at the bit to pull the trigger on the ks8000 that is in my amazon cart right this minute. sorry, i like to help but i wish i had never seen your post.