Floating Sign

I put down some fences and placed a sign on the side of one of the fences. Instead of just the usual slightly disconnected thing that happens, the sign was half a block away in mid air! I was still able to write on the sign.

What I expected to happen was...:
It would go on the fence properly.

What actually happened was...:
The sign ended up floating half a block away!

Steps to Reproduce:
1. Place a fence (I did a fence on top of another fence).
2. Place a sign on the side of the top fence and write on it.
3. Presto! Floating sign in mid air.