Bug #7642 is still present in RC1, I think

I'll explain it again:

The board admin gives a user standard admin permissions. The user (we'll give him the name "Mister X") goes to Users and groups, Administrators, members, and add himself to the group. Than Mister X can much more, because the group Administrators can much more than a standard admin!
Maybe you can make something, that with a fresh install, you don't can manange Special Groups as Standard admin?

(PS: I've tested this with a friend, who absolutely don't understand the phpBB3 permissions...)