I've had two instances occur (in the week or so I've had my B2) of small files (4kb acording to Windows explorer) with a .wav extension. These are in addition to big .wav files which the B2 does compress OK. The small files have the same name as the big ones but with ._ in front.
This is after ripping the CD on laptop using iTunes, because the B2 database can't find the album. It only occurs with some disks however, not all.
After compressing ceases, the B2 still reports n WAV files. Find them using windows explorer and simply delete them. Next time it happens I'll post a screenshot and more detail.