I'm not sure how long, but I didn't seem to be able to get rid of some library tags. In lists, etc, they just held on. They didn't show up in my library on any resource, but they dutifully appeared whenever not needed.
Mystery solved: I earlier bought the OT Discourse Bundle and then refunded it (making sure I tagged it before getting a refund; always important).
Then today, I got the OT HD Bundle which is on sale and half the price of the other one. And .... they came pre-tagged with those mystery tags.
Are we talking efficient or what? Obviously tags don't die with refunds. They live forever.