House cut in half.

Ok, so I was playing Minecraft 1.4.7. on my map with the Adventure Time TP and Mod only. After I spent a good 30 minutes finishing my house, I saved the map. Then I loaded it up later to play some more. The map crashed, so I brought up the map again. Half of my house was gone. And there was a big hole in the roof of the cave. What happened? Was it a rendering error? Any way to reverse this? Help please!