Querying timed out sessions

I use the following XPath contraint on a User entity to retrieve expired sessions. Except that it doesn't work, either due to wrong code, or that I don't have a proper handle on the session scope in a dev environment: [not(System.Session_User/System.Session) and LoggedOn] where LoggedOn we set when the user logs on. The results I get is more closed sessions than there really is. I am still logged in as userX, but this query tells me that userX's session expired.
1 answers

Did you enable persistent sessions?