I made a complex loop of comparators and redstone then I replaced all redstone dust to blocks. When I will replace the last redstone dust it crashed.
I cannot open the world anymore, the game is stuck trying to update the block I put. I have to edit the map on MCEdit to fix the map.
Note that some bots will invalidate this issue because snapshot versions are not signed as release versions.
does this explain what happends to you?
http://youtu.be/_-ctQ3BhwzQ