I booted my desktop this morning and I’ve got some strange hard disk errors. Luckily, of course, I’ve got backups on a second mounted drive (which seems to be fine) and a few other machines I can use in the meantime.
I think I’m going to try a full re-install and see if a full format & disk scan will clean things up. I have no idea what would have caused it. If I learn anything I’ll let you know.
[fsck & e2fsck haven't been able to completely clear up the issue]