As a Linux user, I didn't realise that when I deleted some music files, they actually went into a folder on my SDHC card called ".Trash-$1000" or similar. All of a sudden, the database was showing 2 or 3 copies of each song in an Album. Obviously the excess files were still taking up space on the SDHC card, and I'd have had to deal with their presence eventually, but it might be an idea if the Database can be set to ignore dot folders.
Thanks!