Terrain regeneration after loading world in single-player

There is an area of terrain (dirt blocks and some with snow) that keeps reappearing after I load up the world again to play. If I destroy a dirt block with snow on top, the snow will remain as if the dirt block is still there. Whenever I try to mine or dig these affected blocks, I cannot pick up the blocks whatsoever. They are only destroyed. I tried to use TNT to blow up the area to see what would happen. After reloading the map, the crater fills up in the column of the affected blocks.