wrong timezone precision using plpythonu trigger

Hello,

I am using some code since postgres 8 and testing it on postgresql 9.
Here are the informations about the packages and system used:

# lsb_release -a
No LSB modules are available.
Distributor ID: Debian
Description:    Debian GNU/Linux unstable (sid)
Release:        unstable
Codename:       sid
# dpkg -l | grep postgres
ii  postgresql-9.0                       9.0.1-1
  object-relational SQL database, version 9.0 server
[...]
ii  postgresql-plpython-9.0              9.0.1-1
  PL/Python procedural language for PostgreSQL 9.0


If I create a database using the following code:

-- ========================
CREATE LANGUAGE plpythonu ;

CREATE FUNCTION wrong() RETURNS trigger AS $wrong$
from mx import DateTime

TD['new']['modif_time'] = DateTime.now()
return 'MODIFY'
$wrong$ LANGUAGE plpythonu;

CREATE TABLE pb ( a TEXT, modif_time TIMESTAMP(0) WITHOUT TIME ZONE ) ;

CREATE TRIGGER wrong BEFORE UPDATE ON pb FOR EACH ROW EXECUTE PROCEDURE
wrong() ;
-- ========================

The following code

-- ========================
INSERT INTO pb VALUES ( 'a', now() ) ;
SELECT * FROM pb ;
UPDATE pb SET a = 'b' ;
SELECT * FROM pb ;
-- ========================

produces this result:

#========================
INSERT 0 1
 a |     modif_time
---+---------------------
 a | 2010-10-10 18:30:30
(1 ligne)

UPDATE 1
 a |       modif_time
---+------------------------
 b | 2010-10-10 18:30:29.74
(1 ligne)
#========================

notice the ".74" and the fact that in this example the modif_time of the
modified tuple is earlier than the preceding one!

Best regards

Joël