Well, this is a bug in PG 7.1.1 (and probably previous versions). If you're feeling public spirited, the thing to do is to talk to the PG developers (via the pg-bugs mailing list). They'll probably want a dump of the database to look at.
It would help if you could figure out a way to reproduce the problem reliably. Have you done odd stuff with granting permissions and that sort of thing in the database or is this just a vanilla one-user situtation?
Mucking around with pg_trigger might get you there, I've never ran into a case like this so don't know for sure. But I'd report the bug first and wait for feedback ...
