Can't stop users assigning themselves Admin?

I have users that need the "administer permissions" permission and to assign roles but they must not be able to assign the admin role to themselves or others. I have tried just checking the role I want them to assign and not the admin role but they can still do it.

I am using user protect which prevents them from editing the admin role or deleting it but it doesn't prevent them from assigning themselves the role. I am also using locked permissions so they cannot adjust their own permissions but only change the permissions for other users roles. I thought role delegation might do this. Can someone please tell me if I am missing something here? Can we not restrict users from assigning themselves certain roles if they have the "administer permissions" permission?

Jason