NOTICE FOR MODS
I will be unable to play Minecraft for several months so if you could transfer the report to some other user, it'd be great.

What I expected to happen was...:
The light from lightning during thunderstorms would not illuminate closed spaces.

What actually happened was...:
During a thunderstorm the flashes illuminated closed spaces.

Steps to Reproduce:
1. Make a room or go in a cave
2. /weather Thunder
3. Watch the world and listen for the thunder. The light in the environment will flash brighter, with every thunder even though there is NO way that lighting from the outside world can get in.
4* (optional): Try the same with some torches some blocks away, in order to have dim light. I have observed it with Glowstone and Torches; the flashes are MUCH brighter than the twinkling of the light emmited by the light sources.