Effective permissions not honored by foes setting

If you give the registered users group an administrative permission, such as Can manage styles (so they can switch styles as the same user, for example), but then give a single user a Never permission for that Administrative permission, that user has no Admin permissions. However, you cannot add that user to Foes, because you get a message:

"You cannot add administrators and moderators to your foes list."

In fact, that is the specific permission I tested this with. Somehow, the Foes feature is unable to determine the true permission set of the user under these circumstances.