Previous Track in shuffle mode, and songs that can't be opened
Currently, when you use the Previous track button in Shuffle mode, and the track it picks can not be opened, it advances to the NEXT track after that. So it's like it undoes your request to go to the previous track just because the file is unavailable.
It should be going to the previous track before that, rather then going to the next track.
It might also have the same issue when you're not in shuffle mode as well, but I haven't tested that.