Fences don't render correctly underneath

The connection of fences aren't rendering properly underneath.

What I expected to happen was...:
To not be able to see the sky from beneath the connection of 2 fences

What actually happened was...:
I was able to do it

Steps to Reproduce:
1. Placed a fence
2. Placed another fence next to that one
3. This happened: http://imgur.com/a/ogS2J#0