I was exploring the world in the latest snapshot, and when I came out of a cave system I found two long stretches of no light. There was no structure above them, and upon going in to spectator mode and looking beneath them, there was nothing out of the ordinary there either. The Client Light Level was zero, and placing a torch worked normally. I found a skeleton, a creeper, and a cow in these areas. Nothing else was odd about it, just the light level. I've attached a few screenshots of the issue. 

I do a lot of exploring around my worlds, and this is the first time I've ever encountered this. So I figured it has to do with the snapshot?