Mob spawning ignores light level, biomes and height

Hostile mobs spawn on the surface despite light levels over 7.

 

Testing methodology:  Create a new superflat world.  To avoid slime spawns, I set dirt height to 64, though the effect happens at the default setting of 2. 

Observation: Despite being day, hostile mobs spawn on the surface.  This also happens inside well lit closed areas as well (see attachment).