sunburn effect on picture quality

[Jase Fox]

When im watching standard def on my 50"panasonic plasma (full hd) i notice what i can only describe as a "sunburning look" on peoples faces, when its on a close up shot of faces they seem to have red blotchy patches on them even my 10yr old daughter noticed it as she thought they had red lipstick on there faces, however with hd content it seems fine, so could this interference be due to the fact its standard def on a hd plasma? or a flaw with the plasma? for the record i watch standard def in 576p but no matter how i watch it its still there, has anybody else experienced anything like this?