As far as I know, this is a DVB driver issue. The DVB API seems to only synchronize audio and video on stream start, and not later on. If complete audio or video frames get dropped, then the two streams get out of sync and stay out of sync. This only affects unreliable streams, so it works quite well on most systems.
It would be quite difficult to fix such stream errors before passing the stream to DVB, so I guess this is either a driver or a firmware issue.
Hmmm - this seems to only affect recordings though and not live TV?
My TV, DVB-T set top box etc all don't suffer from this problem and can resync audio/video so surely it cannot be that difficult to address? It is a requirement of all DVB devices..
Cheers,
morf