I have seen a couple articles on this site regarding the problem with form values persisting when using sessions. People find that if they are using sessions, and submit a form, if they hit back, the form values are empty or they get a "Page Expired" message. I have found a way around this - put the following line before your session_start or session_register lines:
ini_alter( "session.cache_limiter", "public" );
Thanks,
Adam Olsen
Webmaster
Western Web Works