BUG #5554: PostgreSQL 8.4.0 doesn't update my table

The following bug has been logged online:

Bug reference:      5554
Logged by:          jose soares
Email address:      jose.soares@sferacarta.com
PostgreSQL version: 8.4.0
Operating system:   Linux Debian 4.3.3-13  64-bit
Description:        PostgreSQL 8.4.0 doesn't update my table
Details:

I all,
I found a strange behavior in my DB, I have a table which Pg isn't be able
to update.
Take a look...

# select esito from scadenziario where id=564481;
esito
-------
C
(1 row)

# update scadenziario set esito='N' where id=564481;
UPDATE 1

# select esito from scadenziario where id=564481;
esito
-------
C
(1 row)

I already tried a vacumm without success,
this behavior is the same for all table's columns.

what's wrong?
thank you for any help.

j