Not a major issue, but kind of annoying. It's also not a crash, so a crash report will not be attached.

Anyway, I had just finished my Iron Golem farm and went to go check on my mushroom farm, when I noticed something really unusual: there seemed to be light, when the debug screen's 'bl' (Block Light) read 0. Also, this 'fake light' made it so I could not place mushrooms near it, although I could in a 'darker' corner.

I did not have Night Vision on, as I don't have the ingredients for that potion yet, so it was plain ol' ordinary vision. I also did not have any Torches or anything placed anywhere near the farm.

What I expected would happen was that the room would be totally dark, as it is indeed underground, and thus I could place my mushrooms wherever I wanted.

How to reproduce:
1. Make a dark room, preferably underground;
2. Plant mushrooms
3. Remove any torches or other light, and block entrance so that it should be 100% dark.
4. Come back hours later, and it should seem as though light is there, even though there shouldn't be any.
It may not work for you because it's so darn strange, but hey.