I am not sure whether this is a bug or bad metadata on the source files and/or whether this has been previously reported.
I was importing a batch of MP3 albums and have noticed that duplicates are not detected during the import. Had a few mis-named albums in different sub-directories. When I imported the top directory, it loaded them twice (I had checked the 'do not import duplicates' box). This does not happen if that album was already previously imported.
From my point of view, the 'export' bug is worse. I set focus, selected 'all', hit 'export'. What I received was :
Artist-name-directory
Album-name-directory
01 TrackA.MP3
01 TrackA1.MP3
02 TrackB.MP3
02 TrackB1.MP3 ....
I.e. Tracks are doubled.
Moral of the story for me : import in smaller batches; be careful before hitting 'accept & import'
