I have comcast cable and was watching an episode of Doctor Who. I paused it to make something for lunch and when I got back I accidentally hit a menu button that brings up an On Demand page. I exited and instead of having me paused where I left off on the episode it took me to the program that's normally playing in this time slot.
So I had the show paused for long enough that the next program would come on. But instead of taking me back to where I was paused on the episode where I could finish it, Comcast will just put you right at wherever the current program is playing.
It won't let you rewind out of the current program.