When opening a world to LAN the client crashes.

Whenever I try to open a world that was created in 13w21a to LAN the host client crashes.

What I expected to happen was...:
I thought the world would open for my cousin seeing as how we were both on the same network.

What actually happened was...:
My client crashed.

Steps to Reproduce:
1. Create a new world in 13w21a
2. Open world to LAN
3. Have another account join the world
4. The host client should then crash after a minute or two