I WOULD LIKE TO REQUEST THAT MY ISSUE IS TO BE REOPENED
So recently I have started building a mob farm designed by Snocrash. This farm works off of normal game mechanics, being that mobs will spawn in low light levels within a certain distance from the player. This farm consists of me building a giant donut-shaped platform at Y=255 using blocks that block mobs spawning on top of them, and block out light. Here is when I noticed that while building my spawning platforms that nothing was spawning because light was coming through the slabs. This bug means that if I were to block myself into a hole and place a slab on top of me, all light will still come through.
I believe this bug also affects stairs as well.
UPDATE!
After one of the mods told me that this is considered normal behavior I knew that wasn't true, in a video by Xisumavoid where he tested which blocks could be placed above a beacon beam, he found that all blocks that are considered "Opaque" (being that, for example, a zombie could stand under and not burn during daylight), and slabs and stairs were under that. I have decided to test this myself and found that even under slabs a zombie will still burn during daylight. I also decided to see if a slab would obstruct a Beacon Beam, and it didn't. Furthermore, in Snocrash's video, mobs are clearly spawning under a slab during daylight. While you could argue that this feature is just something that differs from PC to WIn10/Pe, I do not believe that this is something that should differ.