Video has been slowed down at specific moments to point out the problem, and audio has been removed.
Here we follow a fellow named Kel’Pachi, whose weapon is behaving weirdly at times. Most of his overhead attacks simply freeze above his head, but this is just an illusion. Other players see frozen weapon, but the weapon still hits and kills the opponents. This problem started appearing after the January 2013 patch. This also applies to other weapons. The only pattern here is that it seems that the problem sticks to some servers and some players freeze their weapons more often than others. When freeze occurs it is consistent among other players on the server: everyone sees the same thing. This gives enormous advantage to the player who can find out how to exploit this problem intentionally.