After creating a new user and loging in everything seems to work fine. But as soon as you submit changes to the userinfo, homepage etc. the first ZeroSizedReplies begin (Netscape users know this as "Dcomuent contains no data").
While browsing around in the sourcecode I've noticed that these problems are caused in main(). After saving userinfo, homepages etc. the user.php3 script redirects to itself so it uses the standard main() function.
After this bug occurs in most time the only way to fix it is to go to user.php3?op=logout.