I found something interesting
the setcookie function in ubb.inc.php reads as follows:
setcookie("$name","$value",$time,$cookiepath);
it is missing cookie domain information which is not in any config files either. Having cookie domain information and setting it to ".yourdomain.com" should make it available on both
http://www.yourdomain.com and
http://yourdomain.com. I wonder what Rick has to say:
setcookie("$name","$value",$time,$cookiepath,$cookiedomain) ???