[eluser]Unknown[/eluser]
The session library doesn't clear the active record query cache before trying to update the session record. The obvious problem with this is that you need to manually flush the cache at the end of each controller method, or hit an exception.
./system/libraries/Session.php: Line 281
$this->CI->db->where('session_id', $this->userdata['session_id']); needs to be preceeded with:
$this->CI->db->flush_cache();
