This is still an issue.
- create a tag
#example - try to bulk add it to topics in a category → tag appears in the drop down
- add it to a tag group
restricted - add the tag group as “Restrict these tag groups to this category” for that category
- try to bulk add it to topics in that same category → tag does not appear in the drop down anymore
This is happening because /tags/filter/search?q=&limit=5&filterForInput=true does not even take the category into account.