How can someone be an admin and not be in the admin usergroup?

[Macsee]

An old account on my forums that hasn't been used for years, has returned but he can't seem to login so he emails me.

I do a search in the adminCP for an exact match on that username and I come up with two account identical in every way - same username, same email address, same everything. The only thing that's different is their IDs - the two IDs are separated by a few thousand numbers.

Strange. But it gets worse. When I click on user manager to see the profile, one account is in the Registered usergroup. Fair enough.

The other account's primary usergroup is Administrators.

Alarm bells immediately go off. I went and did a user search and asked for a listing of all users who have the primary usergroup of Adminstrators.

His user's name doesn't come up in the list.

I've tried the search several times. His profile is clear that he's an Administrator but when I list all admins, it's only my name that comes up.

How is this possible?

(I've checked config.php and it's only my user ID in there)