Player cannot leave the swimming animation underwater

Can confirm.

Might be caused by the fix for MC-132064.

Confirmed for Pre5, agreed. I also think it is related to bugfix MC-132064. This might be related to an attempt to fix bumping your head (suffocation damage) when swimming under blocks and accidentally swimming "up". I've not come up with a search term for that bug yet. But while working on the ocean floor, I'm "swimming down into" the floor, no damage, but building becomes an extra layer of complicated as I can't "stand" and work.

Yep, can confirm in Pre5. really annoying, mostly at the time of build something

How to Reproduce

Go underwater, and go into Swim mode, then let go of the controls. You'll see you're stuck in swim mode.

In Addition

When Stuck in Swim mode, when looking up or down without touching the controls, you automatically go up or down.

Side Notes

In my opinion this could also be useful in some cases, you can just literally float there and look around, and it looks cool, but its also annoying...

I appreciate you added in what I put in my duplicate report, as its more detailed. However you could've put your opinion on this bug in Side Notes.

If this is an attempt to prevent people from suffocating while looking up, that still happens, too. So now you suffocate when swimming up, and it's impossible to build under the water as swim mode can't be exited.