Weird partial black line while playing full screen movies

[Doobz]

I have a 27" iMac and recently, while playing HBONow shows/moves fullscreen, I get this weird partial horizontal black line in the video.

It's definitely not my screen, because I don't see anything wrong with other apps and it doesn't show up when I play a movie on iTunes. I've tried playing the videos on Safari, Chrome, and Firefox and I get the same result.

I've included a screenshot.

Any ideas?

 

[webbill3000]

I have the same thing. tried on Firefox and Safari. Netflix and other full screen apps work fine....