There is a bug in the category module (in 0.7). As a temporary solution I had to activate all "inactive" categories (and change the permissions on them to be invisible for the normal registered users).
Yes, this makes sense to me. 😉
Perhaps you can "fix" the Categories Control Panel, so that it is always shown although you are on the bottom of the category-list and switch the save button to this "Box".
But anyway... Nice work you already did with NodeBB. 🙂