Unusual permissions behaviour

I have this problem in 7.1.3 - I can't confirm at the moment if it exists in
7.2.

I have already granted the 'au-dietclub' user delete and insert permissions
on the users_flags table at this point:

australia=> delete from users_flags;
DELETE 0
australia=> delete from users_flags where user_id=1;
ERROR:  users_flags: Permission denied.
australia=> \connect - chriskl
You are now connected as new user chriskl.
australia=# grant select on users_flags to "au-dietclub";
CHANGE
australia=# \connect - au-dietclub
You are now connected as new user au-dietclub.
australia=> delete from users_flags where user_id=1;
DELETE 0

Why do I get a permission denied when I qualify the DELETE statement???

Chris