It can be corrected, set your .htaccess file up to forward users accessing yoru site without "www" to "www" so all users access your forums the same way.
It is intended behavior however that it not function this way, as it's a security issue with cookies (as cookies should not spread over differant domain names, otherwise you could see even more issues).
I'll post something later on about how to configure apache to forward url requests to another url, probably in the chitchat forum or something.
