Nether issues on servers

I was trying to access the nether on my server. When I logged in, the chunks were very, VERY glitchy.

What I expected to happen was...:
When I entered the Nether, it would generate a normal world.

What actually happened was...:
Instead, a bunch of random blocks generated.

Steps to Reproduce:
1. Create a new server with 12w49a (must be a server, the nether works fine in singleplayer)
2. Build a nether portal and enter it
3. Notice all the random blocks