I'm hoping that it was just a messed up database, but I had something really odd happen a few minutes ago...
In a library that I've not had open in a while (about 3 months) I had all except the topmost level of tags in the tags hierarchy disappear. All but the basic tags were neatly tucked away based on their usage in the hierarchy so the net effect was that all of my tags on the about 8000 objects in the library went AWOL. The top level tags are all still there though.
I'm wondering if there's something that changed with the SQLlite database structure (Contents.db), as I'm not able to open the database file in SQLlite manager any more either; it claims the database is corrupted on an unknown format.
Sadly, I don't have a backup of the files that are in this library so the tagging work on those objects is gone for good. No huge loss as it was more of a concept test project than production at this point.