Random holes in my adventure map?

Hey, i put a lot of time in my adventure map. didn't worked on it for 1 week. so i decited to build on it agian. but now the most of my work is gone! a lot of random holes has disepeard? i think it have to do something with the world gen? beguse it is a redstone world with sandstone and the hole goes intuil the grass... and is there any way to get it all back?

Screenshots: http://imgur.com/a/E0cjx