There is a new feature in the last few snapshots, which is that you actually swim when you try to sprint underwater. Sadly, there is a visual glitch that occurs when you have view bobbing on. You see, when you are up against the top of the block, view bobbing occurs, because it thinks you are walking. This happens when sprinting and when not sprinting. It is fine when not sprinting, because you are literally walking underwater. Now, when it comes to sprinting, it does not work, because you are not walking when you sprint underwater. You're swimming. So view bobbing should not happen when sprinting up against the top of a block underwater, because it does not happen when you are in the middle of water while sprinting