I guess I spoke too soon.

I just added a new album and re-ran mp3tofid, and it acted as if I had changed all the files - rescanned every file, and generated a new fid for every song. I was suspicious, so I ran rsync with the dry run option, and sure enough, it wanted to delete everything on the player and start over again.

I am sure this is something to do with me using XFS on my server, but I doubt that XFS randomly reassigns inode numbers whenever it feels like it. I am wondering if I am overflowing anything with the high inode numbers (the latest songs I just added all have inodes in the 373 million range).