My arms and legs disappeared from my avatar after flying with elytra and fireworks in creative mode. I was also diving into the water from flying because it's so smooth diving into water with the new sprint-swimming.

I used a few fireworks, then it they ran out. But I think the game glitched, I rubber-banded back a little bit, the fireworks went for another second or two, then I entered third person to see that I have no arms or legs.

Possibly has something to do with the new animations for sprint-swimming?