Basically I was messing around with FallingSand and /summon, and made a command block that spawns FallingSand Entities that turn into a cake when they land.

I pressed the button and there fell a cake from the sky, just as expected, when I pressed the button again, there fell another cake, but it got destroyed when it hit the ground because it landed on the other cake, everything seemed normal.

However when I quit the world and reloaded it later, the world did not want to start, I tried a couple of times, and then it worked, when I was in the game, the chunk I was in completely regenerated, wiping out my builds in it..

The command I used was:

 /summon FallingSand ~ ~10 ~ {Tile:92,Time:1}