Minecraft stuck on dirt screen on ubuntu?

So i have a Chromebook that has ubuntu (unity) on it and i have downloaded minecraft running on openjdk 6 cause open jdk 7 isn't working for me. Everything works perfectly fine until i either leave a game, go threw a portal, respawn, and more, but once those things happen i get stuck on a dirt screen and i have been looking all over for a fix but i could never find one. I don't know if it is because i have openjdk 6 or what. This problem is getting pretty annoying.