Does your digi camcorders does this to?

How come when you use my digi camcarder(i got a panasonic) to video tape the tv screen, a black shadow shows up across the screen, either on top, middle or bottom? But when I video tape my computer screen, it comes out fine. (I don't remember my samsung ever having this problem though).

Is it technology built into the camcorder that supposed to deter people from video taping shows on the camcorder?