When importing media, occasionally Banshee "hiccups".  It creates a duplicate library entry that points to the same file as another library entry.

For instance, if I imported three songs and this hiccup occurred, The first two sings might be perfectly fine, but the third song "hiccups", and so the library reads it as a second "Song 2", but points to the same file as the first "Song 2".  Meanwhile, "Song 3" is never imported - it was replaced by the duplicate "Song 2".

There seems to be little consistency in when this occurs.  I used to think that doing other processes (editing tracks, playing tracks, modifying playlists) caused the bug, but even when Banshee was doing nothing but importing, occasionally the hiccups occur.  They don't even occur every import - some imports are just fine.  I know this doesn't help in reproducing.  I will say I'm running Xubuntu 12.04 with the latest Banshee available for that system (2.6.0).