When a player starts swimming under water, then releases both "w" and "control" to stop swimming (in either order, it doesn't matter), the player is stuck in the swimming animation instead of standing up.

The game seems to think that you are still swimming. You don't move forwards, but if you look up or down, you will rise or sink as usual, just without the forward movement. Keep in mind, this is all without pressing any keys.

This did not happen in 1.13-pre4.