NOTE: I had to put a game mode, so I chose Survival. In fact, it also happens in Creative. Just a heads-up.

So I was walking around, and I had opened up a new copy of the map (because I had encountered this bug before), and decided to go into Creative to test this bug. I walked over to the snow field, and broke a block. For about 1.5 seconds, nothing happened, and then the game closed out, and I received a crash report. When I played 1.5.1 and 1.4.7, this did NOT happen. I have attached a copy of the crash report (I hope you have Office).

Steps to Reproduce:
1. Use MC Edit or some other program to edit in a large, FLOATING snow field (it HAS to be floating. Very important.).
2. Go into either Creative or Survival (it doesn't matter either way).
3. Break one of the pieces of snow.