Tags - When ACL denies creation, Author can still enter them (even though they aren't accepted)

I set my EasyBlog ACL so my authors can't create their own tags (I want them to stick to core defined ones).... Trouble is, it looks like Composer still asks them to type a custom tag... and lets them do it.. it doesn't show at any point that (a) they can't or (b) if they do, that it won't work.

Is this supposed to happen like this? I would have hoped they would have just been shown the existing available tags for use, and simply not allowed to type their own....