Data integrity problem !!!

Hi,

we run PG database successfully for 5 month. There were no problem until
now. I set night maintenance script 14 days ago. It does only this:

VACUUM ANALYZE

I've tried restore database today and strange error come:

Cannot insert a duplicate key .......

I've started investigate a cause and I've found that there are really
duplicated PK in table and some data in the same rows are corrupted. I
I've checked all log files and database backups and found that this
problem arose probably after run VACUUM ANALYZE command which is executed
every night. Everning DB backup was ok and morning backup contained these
errors. There were no user activity between these 2 backups except VACUUM
ANALYZE command. I've inspected another database backups after this event
and I've found that there are some additional minor data curruption after
night execution of VACUUM ANALYZE.
We run PG 7.2. There are no errors in log files and whole system looks ok,
except this :(.

Regards,

Vaclav