I updated my Minecraft to 1.4.2 and my server that i run on my computer and when i killed the ender dragon I teleported back to the over world and then there was only one chunck loaded and i can not interact with anything not even the ender portal i can swim in lava it does not hurt me. so i put the world in my singel player and same thing, my world is completly unpalyable i can not do anything. It also takes forever to load up the world compared to everything else. After 1 min the world loads just a bit more but when i go back in it it goes back to just one chunck.