php sessions files incompatible? - php5.2 debian lenny vs php5.3 debian squeeze

php is truncating the session files to zero after migrating the session files from server one (debian lenny php 5.2) to the new server (debian squeeze php 5.3).

i create a session on server one with createsession.php (see below) and can view the content of the session with dumpsession.php on the same server.

after copying the session files from server one to the other server and switching to server two by changing my local hosts file, i have still the same cookie with the correct session id stored in the browser, the new server accesses the right session file, but instead of displaying the content of the session, the server truncates the session file to zero and starts a new session with the same session id.

is it possible to migrate the session files? is the serverip somehow hashed into the sessiondata?

is session sharing between php5.2 and php5.3 possible?

createsession.php

<?php
  session_name('mysession');
  session_start();
  var_dump(session_id());
  var_dump($_SESSION);
?>

dumpsession.php

<?php
  session_name('mysession');
  session_start();
  var_dump(session_id());
  $_SESSION['foo'] = 'bar';
?>

php.ini session part

[Session]
session.save_handler = files
session.save_path = "3;/var/lib/php5"
session.use_cookies = 1
session.name = PHPSESSID
session.auto_start = 0
session.cookie_lifetime = 0
session.cookie_path = /
session.cookie_domain =
session.cookie_httponly = 
session.serialize_handler = php
session.gc_divisor     = 100
session.gc_maxlifetime = 5184000
session.bug_compat_42 = 1
session.bug_compat_warn = 1
session.referer_check =
session.entropy_length = 0
session.entropy_file =
session.cache_limiter = nocache
session.cache_expire = 180
session.use_trans_sid = 0
session.hash_function = 0
session.hash_bits_per_character = 4
url_rewriter.tags = "a=href,area=href,frame=src,input=src,form=,fieldset="

edit: my solution was switching back to debian lenny.