2 Accounts with Same Name bug since Upgrade

A Youtuber called MCDoenerHD found this Bug:
Since you have Upgraded the loginservers on 10th May, you can fly, get not banned, you can have Godmode or you get free ranks. If it doesn't get fixed, the Servers are full with Hackers! Admins on Server can't ban Them, so They can't do anything. Hopefully you will fix it!