Player positioning is very glitchy, and I'm assuming it is calculated on the hosts end, which is a problem, because it causes snapping, when the host thinks a player is in one place, but the players client says its in another and when the player sends its information to the host it snaps to where it actually is. Causing glitchy movement, this bug can be replicated by going in EDU mode on a world, giving someone the /ability to fly and putting them in survival, and asking them to fly.