Certain animals (cows, sheep, horses, wolves, ocelots, mooshrooms, pigs) drown themselves.

What I expected to happen was...
My cows would have a nice pool party and be very happy swimming together.

What actually happened was...
Some eventually stopped swimming and sank to the bottom. Sometimes they swam to the surface again, sometimes not, they started drowning and died.

Steps to reproduce:

1. Make a pool (a 7 by 7 and 2 deep design, with edges to high to climb up - like I made on 1 of the attached screenshots - you can variate the size)
2. Spawn in the animals (+/- 5)
3. Wait a little bit (within 5 minutes at least 1 dies)