Follow-up to AO3-5615.
Log in as a tag wrangler
Hi, username! > Tag Wrangling
In the "Fandoms" column of the table, follow the link to one of your fandoms.
In the sidebar, there is a list of tag types (Characters, Relationships, Freeforms). Follow the link for one of those that has a count greater than 0 to access the fandom's "bin" for that type of tag, e.g. the character bin.
Follow the "Edit" link for one of the non-canonical, non-synonimized tags listed in the table.
Check the "Unwrangleable" checkbox and press "Save changes" to mark the tag unwrangleable.
Repeat steps 2-4 to access the same "bin" once again.
Follow the "Unwrangleable" link to access a table of just the tags you've marked unwrangleable (of that tag type and in that fandom, of course).
In the "Manage" column, check the "Remove" box for a tag and press "Wrangle."
The tag is removed from the fandom and remains unwrangleable. This makes it impossible to find.
What should happen
You should get an error message telling you you can't mark a tag unwrangleable if it doesn't have a fandom. Better yet, you shouldn't be able to check the "Remove" box.