Did you do a proper burn in when the TV was new?
When my plasma was new, I ran it for 200+ hours on different colored slides. This aged the pixels very evenly and made it "work in" so to speak. I can play games with HUDs, 4:3 content, and movies, and none leave in a burn, even after 3-4 hours.
What you are probably seeing isn't burn in quite yet. Burn in happens over a longer period of time. You are probably still seeing ghosting, which will occur to some degree after anything you watch on a plasma. Just run that built in scroller for a while and you should be fine.
If you want more info on the slides,I can probably hook you up with them. I got them over on the AV forums.