What I expected to happen was
My 1.8.7 map to update to 15w31a

What actually happened was
I wanted to play my 1.8.7 world on the latest snapshot but then an error code keeps popping up.

Steps to Reproduce:
1. My map is on 1.8.7
2. Then I decided to change the minecraft_server.jar to 15w31a
3. I tried to join my server and I got a very long error code (Image tagged)
4. When I just opened the world in my saves, all of my armor stands and signs were messed up, with punctuation all over the signs and my armor stands arms and heads were not in the correct position.
5. Because my world is a world based on the things you can create in minecraft I would love if I could be able to move it on to 1.9, with the new feature