Bug, Feature, or what else?

Hi,

i have created a normal user (no superuser) akretschmer01 and another normal
user ak02. All fine.
The first user is the owner of the db.

As user akretschmer01 i granted:

-bash-4.1$ psql -U akretschmer01 db115150
psql (9.1.8)
Type "help" for help.

db115150=> grant all on schema public to ak02;
GRANT
db115150=> commit;

There are no tables or other objects createt as user ak02.

Now i switched to user postgres (superuser):

-bash-4.1$ psql -U postgres db115150
psql (9.1.8)
Type "help" for help.

db115150=# drop user ak02
db115150-# ;
FEHLER: kann Rolle »ak02« nicht löschen, weil andere Objekte davon abhängen
DETAIL: Privilegien für Schema public

(role ak02 cannot be dropped because some objects depend on it, Detail:
privileges for schema public)

I can revoke all on database from user:

db115150=# revoke all on database db115150 from ak02;
REVOKE
db115150=# drop user ak02;
FEHLER: kann Rolle »ak02« nicht löschen, weil andere Objekte davon abhängen
DETAIL: Privilegien für Schema public

but still i can't drop the user.

I can do that with 9.1.8 and 9.1.1 too, same problem.

How can i drop a user as SUPERUSER (!) with all privileges?

Regards, Andreas