Ah! Yes, the infamous "Black Bar".
It happens because of the relative refresh rates of your TV and camera. The TV does not display a constant picture, it "flickers" very quickly, at a certain frequency called your TV's refresh rate. For a standard TV, this is 60 times per second. (For you techies reading this, I'm ignoring the whole interlaced vs progressive scan thing)
Your camera is also not taking a constant stream of video. It takes a single picture, saves it, then takes another picture, saves it, etc... very quickly. What will happen sometimes is that the two frequencies match up perfectly (at 60hz) or some multiple thereof.
So the camera always happens to take a picture of the TV at that exact moment where there is nothing displaying on half of the screen. Then when your camera goes to take the next picture, the same thing happens. And the result is an apparent "Black Bar" over the picture.
Cool, huh?
