Can't load Custom world

Put the summary of the bug you're having here

Ok so, I've download the new snapshot to test new Customization of worlds, trying to make a superflat world. I perfectly loaded the world (even if 7 minutes)

I loaded world and.... blocks don't appear.
Steps to Reproduce:
1 Download snapshot 14w25b
2 Create a new world with 'Custom' world type
3 In 'advanced settings' set all 'Noise' customization on minimum
4 That's what should appear