Describing the issue:

Breeding large quantities of animals (all animals as far as I'm aware) at once in a 1x1 hole will give about 30% more babies than it should.

Steps to Reproduce:
1. Put 200 cows in a 1x1 pen with water at their feet
2. Feed them wheat as fast as you can, but count how much you've given
3. Count the cows, there may be more than you should have gotten. It is sometimes difficult to reproduce using this method.

I made a video showing this issue here. You can also download the world I used from the attached files.