Dunno if this is a recent bug or I just never noticed, but when typing in a new tag on some random pic, I hit backspace to delete everything I had typed in already, and held it down since, as I remember, it would stop having any effect when there were no more characters in the new tag’s little text box. Instead, it started deleting the existing tags before it.
Otherwise, the tag box thing is much better than the usual “naked” text box from other boorus, so kudos. The only improvement I can think of would be the possibility to edit a tag box, but it’s no big deal.