I have been building a lighthouse with a highway running by about 2000 blocks south of the natural spawn. The chunk with the lighthouse on it has reset to it's default state twice, resulting in having to rebuild pretty much the entire thing. The second time it left some random planks and glass panes intact, but still deleted most of the lighthouse. This has happened two times within a 3 day span now, and seems to occur mostly after leaving the game on for more than three consecutive hours. There are two pens with about 10 sheep each nearby, but no redstone mechanics or other processor heavy mechanisms or group spawns that would overload the engine, however it is a pretty heavily developed world that spreads over a large distance. This problem has only been encountered in one specific location on the map, and only on this map. Included is a screencap of what the lighthouse looked like immediately after the second reset. I did not have a picture of the completed lighthouse as I had not quite finished rebuilding it after the first wipe, and it was not quite complete to begin with (it was about 90% done before initial reset).