Mob spawning seems to ignore light level at times.

I have witnessed mobs spawning at night in areas that are well above light level 7.

Most recent was a creeper spawning on a block that was light level 12.

The creeper spawned in between the columns of chests against the wall there. Its light level is 12. 

This happens pretty regularly in my "base" area. Its very large, and completely lit up.

This one is hard to verify as you usually don't actually see them spawn to often, you just round a corner and boom creeper blowing off your face, or a skeleton pinking away at you. However the distance they would have to walk to get there from a "dark" area is over 128 blocks.

I watched this creeper spawn right there in the SS. Went over, killed it and checked the light level, its 12, so i grabbed a screenshot cause I'm getting tired of this. I didnt put in all this effort to make a safe base to avoid having creepers blow my stuff up, just to have creepers blow my stuff up.

This happens A-LOT. Creepers are the most significant offender, however skeletons and zombies do it as well.

There are also other conditions that mobs will spawn in they should not, I have watched creepers, zombies, skeletons, and zombie pigmen spawn on stone half slabs (bottom half). This is separate though so ill make another ticket for that.