[mod_python] Session subdomains

I'm using Debian etch (Mod_python Version: 3.2.10-4)

I want to use the same session for xx.mydomain.com and yy.mydomain.com

In documentation (4.8.1) shows:

"In order to have a session which spans across common sub domains, you 
can specify the parent domain using the 
mod_python.session.application_domain  option ("PythonOption 
mod_python.session.application_domain mod_python.org" in server 
configuration)."

I put: "PythonOption mod_python.session.application_domain mydomain.com"
in virtual server apache file.

Ok, just done that, but... it did'nt work
Then i read the variable with req.get_options() and it's set!

I login in a subdomain, xx.domain.com and all works ok, i have a 
session, but when i change to the other subdomain i'm not logged in, the 
server sends my another session.

(in firefox-web developer-Cookies i see the two different session 
cookies established, one for each subdomain: HOST xx.mydomain.com and 
HOST yy.mydomain.com)

Can't version 3.2.10 do that?
I'm doing something wrong?

THANKS
Rubén