A diamond moderator rolled back a question to a state where it had homework. This effectively recreated the tag, despite it being blacklisted.
This should not happen, and is not the only tag-related rollback bug.
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OH NO QUICK GET EVERYTHING OF VALUE AND GET OUT BEFORE THE PLACE BUR...
It's still blacklisted, so it can't get back in through the efforts of a human being typing it; the most annoying thing that could happen is a post becomes edit-blocked until someone removes the blacklisted tag.
This shouldn't have happened, I distinctly remember Shog9 taking an axe to homework just like I recently did to logic:
But, that obviously doesn't scope previous revisions. I'm going to look into it. It's not uncommon for us to blacklist a tag just to stop the influx while communities go to work removing it carefully, which can be an edit blocker (we're not fond of that, but that makes fixing this sort of weird).
Unceremoniously and silently dropping a blacklisted tag from a question during a rollback makes the most sense, but I need to think about that and find out just how possible that might be. Homework synonyms become quite interesting too, in the context of the other bug that you linked.
In the mean time ...
... and stay tuned.