Also mentioned in MC-132286, but in which the problem is marked as solved.

Problem:
players has a swimming animation when sleeping.

How to Reproduce:
method 1:
place a bed,and then sleep. you can see yourself swimming on the bed.
method 2:
join a multi-player world, then let someone sleep. you can see he is swimming on the bed.
(P.S. underwater is NOT necessary in both methods.)

Expected:
player shouldn't swim.