EDIT: This is line bleed, apparantely. Can anyone compare a G20 or G25 to a ST50 in terms of line bleed? Seems like this is inherent to plasmas.
Been noticing for a while that my P50G25 has an issue with horizontal bands. Only today when watching a DVD did I really look into it, and realize what it was. The issue is that if you have an image with a bright object - for example a face, surrounded by a dark area, the light area appears too light.
For an example,
The area highlighted in read in this image looks overly bright. Now, this appears to be because of the long dark horizontal line formed by the windowpane behind it. As the camera moves, causing that windowpane to move downwards in the frame, so does the overly bridge band.
Now, I tried this on a PS3 and a XBox, and on other content, and different HDMI cables. In all cases, it's horizontal and still there. Since it moves, this cannot be image retention. Blinds being in the frame also produce a similar effect.