multiple session cookies with session library

[eluser]Tom Vogt[/eluser]
Any help appreciated.

There is one and only one place in the code where I call set_userdata:

Code:

public function login($User) {
  $this->ci->session->set_userdata(array(
   'user_id' => $User->getId(),
   'client' => $this->ci->config->item('client')
  ));

and my session config is:

Code:

$config['sess_cookie_name']  = 'cisession';
$config['sess_expiration']  = 7200;
$config['sess_expire_on_close'] = TRUE;
$config['sess_encrypt_cookie'] = TRUE;
$config['sess_use_database'] = TRUE;
$config['sess_table_name']  = 'ci_sessions';
$config['sess_match_ip']  = FALSE;
$config['sess_match_useragent'] = FALSE;
$config['sess_time_to_update'] = 300;

My application is AJAX-heavy, and I'm using the URI routing feature quite a lot. I'm very certain that my download is not corrupt. I'm using CI 2.1.0

If anyone has a clue on where to start looking - let me know.