I really can't find a pattern to this, so I can't give a finite way to reproduce this (i.e. number of songs in an album, etc.), but I can explain it.
When I build or rebuild the tagcache, several songs will be displayed twice, yet, it's the same file. This doesn't happen to every song, and the problem is album specific. Either all the songs in the album will be displayed twice (or in some cases, threee times), or everything will display fine.
For example, I've got several albums by John Williams. The tracks in the Star Wars albums will display twice if I look at said albums, or view all the tracks by John Williams, however, the other two albums (Jurassic Park and Memoirs of a Geisha) display fine. None of the tracks are displayed twice.
However, there's several artist/albums that show up fine with no problems.
FS#5594 has a bug entry that's similar to this problem, but not entirely.
Anyway, if anyone could help, it'd be nice.