Fly with elytra into water without touching the ground so the elytra are still activated. While holding space, look straight up. The player appears to sink into the ground very quickly and the world then stops with the error "Invalid move player packet received". Reloading the world puts the player back into the water. Sometimes the world reloads with the player underground again and creates an endless loop that renders the world unusable.

Note:
The attached screenshot shows "Back to server list" but this bug happens in a Singleplayer world. I haven't checked multiplayer.