Once dubbed as an iTunes-killer, Songbird has been plagued with bug issues—the most recent involving a nasty bit of business with its iPod add-on. Apparently it deletes music without user permission.
Naturally, it is highly recommended that you uninstall the add-on. Songbird is currently working on the problem, but if you have already been bit by the bug and you don't have a backup, it might be a good idea to look into some free software tools for recovering deleted files. [Songbird via Lifehacker]