There have been a number that have had it. Some it's never gone away, one or two, it seemed to go away after a period of time.
It's the same software as on that HD box, so it would have to be hardware... But the good majority of users I have heard from don't have the issue, so it's not global... Not sure if its a the box not likeing certain tvs ect.
Depending on your exact issue.. no it hasnt been fixed yet.
The NB3, though seems to do it LESS now with recent updates, it still does it... MOST of the sound distortions, are likely from when the NB3 switches from DD5.1 to PCM2.0 Depending on the reciever its into, or even a TV if it has a virtual surround, etc.. can react differntly and the sound change in how its outputed between the two modes.