Recently I banned people from our clan server only to find they are able to get back in after a few minutes.
Apparently there is a XUID spoofer out there that the cheating f^*kers are using to change ip to allow the ban to be removed. (It will only allow people with dynamic IP's to change it, so those with static are still stuffed). You can re ban them but will end up having to redo when they keep coming back.
Simplist solution I have found that if this happens just add their name or part name to the badnames list (make sure you enable it in your config file) this will hold them out a little longer, hopefully for good or until they change their name. :banned: