I have not tested this extensively, but I have noticed RH 6.0 (every update installed) wu-ftpd 2.5.0-2 not clearing utmp/wtmp properly with anonymous ftp logins. This can be noticed best with 'last', where every single anon login is 'still logged in'. Regular users work fine. I have not tested this extensively, but I guess the problem is quite widespread. I have changed GID 101 (console in my case) to 91 because GID's above 100 are in general use by our company but I don't think that affects anything since the group console doesn't even own any files in our system..
*** This bug has been marked as a duplicate of 3482 ***