Steps to reproduce
Make a large, fully dark area.
Place two light sources such that they create two spots with light level 1 next to each other.
Place a solid block in a location that reduces one of the light level spots to 0.
Expected result
The other light level 1 spot remains light level 1.
Observed result
The other light level 1 spot changes to light level 0, allowing monsters to spawn.
Alternate steps
Load
Press the "Reset light" button.
Press the "Place blocks" button.
Watch the north side of the snow for a few minutes.
Expected results
Nothing spawns north of the snow because the torches to the north are 14 blocks away, so the block light just north of the snow should be at level 1, and it is at level 1 before the snow is placed.
Observed results
Monsters spawn on the blocks north of the snow, where block light should be 1 but is miscalculated to be 0 after the snow blocks are placed. See
[media]
This may be related to the fix for MCPE-145828. I am not sure if it happened before 1.18.1 or 1.18.2.
OTOH the error here in changing what should be a 1 to a 0 when multiple sources are involved is similar to MCPE-81981.
This bug especially impacts spawnproofing around monster farms because the new requirement of block light 0 for spawning means light sources must be placed in exactly the right spots to block spawns outside of a spawn area while not allowing any light into a spawn area. For example, I discovered this bug while testing a farm that uses ice floors. I need to use minimal light in order to spawn proof the sides of the item stream coming out of the bottom of the farm while not allowing light to bleed through the ice floor.