Animals seems to think they can find a path to unreachable places

What I expected to happen was...:

See the animals walk in the delimited area. 

What actually happened was...:

Instead, they seems to focus on the border of the enclosure

Steps to Reproduce:

1. Create an enclosure with 1.5 height (A bloc and a slab) (Follow the images)
2. Put cows inside
3. Notice that the cows will focus on the borders (If they move, it's only to go to another one)