two records with same oid, freak accident?

in some sort of freak accident, we've ended up with a duplicated
record.  all info, including the oid was duplicated.

it was during an update, two people ran a command at the same time.

user 1: BEGIN
user 1: NOTIFY
user 1: UPDATE
user 2: BEGIN
user 2: NOTIFY
user 1: END
user 2: UPDATE
user 2: END

same command, so the queries are the same.  the record duplicated was
the one being updated.  i'll try to reproduce it.

also, I had a unique index on the table, but that didn't seem to make
any difference.

any ideas on how to delete one without deleting both?