Duplicate key

I'm running Postgres 7.3.3 on a Linux Box
I know that seems impossible,
that I can not replicate the bug but
today without hardware failure, power down etc etc
I had a duplicate primary key + a duplicate unique index
on one table. I already had this "kind" of problem in another
table and I solved the problem not reindexing anymore that
table, now this table have 12 index and is eavely updated/inserted
so I must reindex this table once in a day.
Are we sure at 100% that the is not a reindex fault ?

What can I do next time in order to discover this nusty bug ?

BTW, I don't know if you got my past email about a strange
core by the postmaster that disappeared after that I change
the scheduling of a vacuum ( not anymore togheter with the
select that was causing the core ); well after almost 2 month
I still not having another core.

Regards
Gaetano Mendola