Have you run the scroller to try and get rid and have you set the pixcel shift ?
I have a PN50a650 plasma. I have had if for a few years now. Lately I have noticed in the bottom right corner of the screen one of the station logos(Nick Jr). My daughter probably watches this channel an hour or 2 over the course of a day. Now, I only see if when that area of the screen is black. The logo shows up reddish and is surrounded by some other reddish blobs. The logo does seem to fade a little over time but this is something I have not noticed until recently. Any ideas? Does not sound like a normal burn-in issue because you can only see it on a black screen.