Lighting engine broken?

Created new world, opened inventory, gave myself a sapling and the world turned black. Lighting engine broken?

What I expected to happen was...:
World would stay light/visible

What actually happened was...:
World turned black (carries across to other worlds, menus/chat/everything else works/looks fine)

Steps to Reproduce:
1. Load 13w43a
2. Create new world
3. Use creative to give yourself a sapling

Image 1: The issue I'm on about, note the game version in the top-left
Image 2: The same world but an older snapshot, note the version in the top-left