Staff-only tags shouldn't count toward tag limit

We have staff-only tags, which are configured thusly:

I just had to remove a user-applied tag to be able to apply a staff-only tag for correct routing/attention.

I think the user is unlikely to notice, but if he does come back to the tag list, I believe he’ll find a set of 4 tags, and a warning that he can’t add any more tags because only 5 are allowed.