Everyone knows that mobs cannot spawn on top of bottom-half slabs. But in this specific case mobs hardly spawn at all below solid opaque blocks with a bottom-half slab on top of it. This somewhat relates to
MCPE-12422 and now-fixed MCPE-11112 but is clearly not the same.
Steps to reproduce:
- Build a 12x12x3 spawn chamber out of any kind of solid opaque blocks.
- Optionally place tripwire and redstone lamps to ease observing mobs inside it.
- Take 24 blocks away from it and wait 10 seconds or so.
- Observe that mobs start to spawn in the chamber.
- Now cover the roof of chamber with any kind of bottom-half slabs.
- Take 24 blocks away from it and wait for mobs again.
- Observe that the spawn rate has severely reduced. Now it takes several tens of minutes to spawn even a single mob.
What I expected:
Slabs on the roof do not affect the spawn rate at all.
Note that the inner height of spawn chamber needs to be 3 blocks or higher in order to trigger this bug. If it's only 2 blocks high, slabs don't affect the spawn rate as expected.