penders - 7:00 pm on Feb 20, 2012 (gmt 0)

Could it be as the logout script kills the session it removes my previously set up 'referer'

That's quite probable. Depending on your script you don't necessarily have to destroy the session in order to log a user out. Simply deleting the specific vars that authenticate the user could be sufficient?

I'm still learning about sessions and have no idea what session register does :s

The PHP manual is your friend ;) .... session_register() [uk.php.net]