Having had two Panasonic DVD recorders I am well aware of this problem. I had the problem originally when I wanted to record Virgin Media channels and it did only record what was on the tv screen at the time so when the tv was switched off it recorded nothing...
I could not find an explanation or cure for this on the web at the time so I bit the bullet and upgraded to Virgin+. Now I'm on my second Panasonic DVD recorder and use it to tape off freeview, which it does well, and with the tv off. So it may well be a legacy issue with your old recorder. something they fixed with later models.