Affects Version/s: 1.15.2, 20w19a
Fix Version/s: None
Although enderman can place pumpkins on top of snow to create snow golems, the same cannot be done for wither skulls to summon the wither. For the same reason, repeaters/comparators don't update their power state when placed.
1. Download the provided world. It adds wither_skeleton_skull to the enderman_holdable block tag, allowing endermen to pick it up. It adds air to the wither_summon_base_blocks block tag, allowing the wither to spawn almost anywhere.
2. Place a wither skeleton skull manually next to one of the many piles
→ The wither spawns and is immediately killed by the running command block
3. Wait for an enderman to place down the skull it's holding
→ No wither is spawned
Endermen just call level.setBlock to place the block in their hands. This skips Block#setPlacedBy, which several blocks use. It's usually for transferring item data to a block entity (endermen store neither of that information), but some blocks like wither skulls and repeaters rely on this function to update their state.