In 1.11 is was made so that creepers would be able to spawn in a 1.8 block tall area (under upper trap doors) this would normally allow for creeper only farms, a thing that bedrock desperately needs and has needed for years. Anyway, the issue is that everything spawns under trap doors now. Zombies, witches, skeletons etc.

Only creepers, spiders and i think baby slimes should be able to spawn in an area under trap doors.

How to reproduce.
1. create a flat world, keep it daytime.
2. make a 32x32 room of solid blocks, so that its completely dark inside. The room should be two blocks tall.
3. put any kind of upper trap door on the ceiling
-this should allow you to walk under it just fine
4. observer as creepers, spiders, and zombies all spawn under the roof and walk around freely.
Only the creepers/spiders should ever spawn

It has become pretty apparent that bedrock doesn't have proper hit boxes for most mobs, for instance you cannot prevent spider spawns as they spawn in a 1x1 area. When fixing this, it would be amazing if at least the hostile mobs in bedrock where given a proper hitbox, like those of java.