Put the summary of the bug you're having here

What I expected to happen was...:
I expected that when I had the animal leashed that it would just tie on the fence

What actually happened was...:
When I placed a fence on top of the other while the animal is leashed, the fence on top will disappear and the animal will be tied to the bottom, and when you break the bottom fence it will drop 2 fence blocks. 

Steps to Reproduce:
1. leash an animal
2. place a fence on the ground
3. put another fence on top of it

4. after the fence on top disappears break the bottom block and you will retrieve 2 fences