See http://musicbrainz.org/search?query=jasrac&type=tag for example. "jasrac-no-iswc-onlu", "wrong jasrac credit s", "not in jasrac yet" and "jasrac-no-work" all have no results (and haven't had for quite a while now) but are still showing up there.
Maybe I've found a related issue.
In this release-group, you can see liste de courses jpn and liste de courses tags.
Those really look like tags of mine, I highly doubt someone else would use that.
But on this RG, my tag is now only liste de courses jpn (2).
If I use one of these tags, the usage count goes 2.
The old tags are still there, associated to a ghost?, although I guess no one has used them (but we can't see who tagged any more, right?).
Please open a new ticket for the behavior you are seeing, it's not about this ticket.
I thikn it has to do with the « garbage collect » part of this ticket, maybe.
What you're seeing is not a bug at all. Someone else has used those tags - http://musicbrainz.org/user/erpbridge/tags/liste%20de%20courses and http://musicbrainz.org/user/erpbridge/tags/liste%20de%20courses%20jpn
Agreed to fix within 12 months by http://scheduling.ocharles.org.uk and http://chatlogs.musicbrainz.org/musicbrainz-devel/2012/2012-03/2012-03-26.html#T19-36-54-3898
In review at http://codereview.musicbrainz.org/r/2245/
This is in the beta branch, but these changes are only on the database, so they can't be tested until we deploy in 2012-09-17.