Black Box over TV Image

[toomuch]

My 921 is connected to a media pc, so it's on all the time. Many times I find that there is black box over the TV picture, the black box does not cover the whole picture, so you can see the "real" TV picture behind it. Switching the DVR on and off solves the problem, but half the time the media PC already recorded the screen with the black "box" over it.
any suggestions?
(I am on my third 921, but I paid $1000 for it, so I am sticking to it)

[Sandman]

Do you have close captioning turned on, it has happened to me accidently

Bob

[Michael P]

This happens to me too, and I'm connected to an SD Sony Trinitron. It was worse with L331.

[sciggy87]

Happens to me too, started with 330