Panasonic DVD HD recorder

Did you change anything before this started happening? Anything, like add an A/V receiver, mess with the cables, added an input to the DVD recorder.

If not then it sounds like (no pun intended) you have a problem with the DVD recorder. I have 2 panni DVD Recorders and both support playback of something recorded while recording something else at the same time and like you did before, I only get the playback sound.

Now on mine I have each recorder hooked both directly to the TV and to my A/V receiver as many times I don't turn on the home theater to watch say the news. But since I am hooked up that way, if my TV is selected to DVR and my A/V receiver to the Cable Box then I will hear the DVR from the TV speakers and the Cable Box channel from the home theater speakers.

I suspect something is wrong with your DVR though, I have never had it literally record both the sound from what I was playing and recording on a single recording so when I played it back both were there. I also can't imagine how you could even get it to do that if you wanted to unless everything was hooked to your A/V receiver and it has some kind of mixer function.

Sounds like it time for a trip to the repair shop. One thing you might try first is unplugging your DVD for a couple of days and then plug it back in and see if the problem goes away on its own.

Good Luck!