When going into the 14w26c snapshot, the command blocks loose the commands and blocks disappear.

Put the summary of the bug you're having here

What I expected to happen was: the blocks would be there and the commands in command blocks would have been there.

What actually happened was: There were no blocks in the world and then when I went into previous versions (14w26b) the command blocks had no commands in.

Steps to Reproduce:
1. Make a world in 14w26b (or lower versions) and then place a command block with a command in it.
2. Go into 14w26c and then everything would have gone.