This bug happens when riding a camel, horse, or mule across water.
Expected behaviour
The animal either swims across the water regularly, or sinks and dismounts the player (as it would in previous versions of the game).
Observed bahaviour
The animal bounces up and down, and the more it swims, the more it bounces up and down.
The player is only dismounted when the animal bounces so much that the player is completely submerged when the camel falls back into the water.
To reproduce
Get a camel and saddle it
Steer it towards a large pool of water
Sprint into the water
This also affects horses