Log in as a wrangler
On the New Tag page, create a canonical tag and remember its type, e.g. Meta Character Tag 1. This will be your meta tag.
Post a work with another tag of the same type, e.g. Sub Character Tag 1. This will be your sub tag.
From the edit page for Sub Character Tag 1, canonize the tag
Again from the edit page for Sub Character Tag 1, add Meta Character Tag 1 as a meta tag
Bookmark the work you posted earlier
Wait a few minutes
Yay, both the work and the bookmark appear on Meta Character Tag 1's work and bookmark listings
From the edit page for Sub Character Tag 1, decanonize the tag
Wait a while
Uh oh, the work and bookmark still appear on Meta Character Tag 1's work and bookmark listings
What should happen instead:
The work and bookmark should be removed from those listings.
It wouldn't hurt to test bookmarks of works, series, and external works. Definitely check that a work/bookmark does not get removed from the tag listing if it is also tagged with Meta Character Tag 1 or another tag that is subbed to Meta Character Tag 1.
Also, make sure to test this with the “Make tag non-canonical and unhook all associations” option as well. You’ll have to be logged in as an admin to use that.
This happens because decanonizing a tag does not remove any filter taggings it inherited from meta tags.
This is the work when both Sub Character Tag 1 and Meta Character Tag 1 are canonical:
The filter tagging with filter_id 1218470 is Sub Character Tag 1. The inherited filter tagging with filter_id 1218467 is Meta Character Tag 1.
This is the work when Sub Character Tag 1 has been decanonized:
Note that the filter tagging with filter_id 1218470 (Sub Character Tag 1) is gone, but the meta tag's filter tagging remains.
Please refer to tickinginstant’s comment about the “Make tag non-canonical and unhook all associations” option for information on potential race conditions when using that option.