Small bug mainly blamed to Notch in fact all Notch but with the Quantum suits it's pretty much broken to hell. You can do the hop 3 high down a cave for example and move so fast that you can run past the chunk loading throttle and also do a lot of damage to servers causing massive amounts of chunks to be forced loaded and known to cause memory leaks from it. Really abusive exploit for large servers.
It is a vanilla bug like I said enhanced 10 fold with the suit. Not sure if it's worth the time investigating or not.