Mobs are spawning blocks at Y=255 during daytime and during nighttime despite the area being lit up.

Steps to reproduce:

• Make a wide plateform at Y=255 (build limit) using a spawnable block (e.g. stone)
• Set the time to noon
• Be sure to be at spawning distance from the platform
• Observe

Plus Zombies and Skeletons don't burn from the sunlight (unless they walk on transparent blocks.  [Tested with glass])