The bug
The recent spawnEvent option in /summon creates corrupt mobs the majority of the time. It causes the regular minecraft:entity_spawned to be skipped, which many mobs rely on for initialization. Mobs that skip this event are permanently broken or corrupted, each in a different way depending on how that mob behavior is implemented.
How to reproduce
1. /summon sheep ~ ~ ~ 0 0 wololo
2. Try to shear the sheep
→ ❌ You can't, this mob is missing a bunch of components that were supposed to have been applied by the entity_spawned event. It is now broken permanently.
Notes
Even if the specified event is run after entity_spawned, it would still be possible to create corrupt mobs, for example a chicken that has both adult and child components at the same time. Most mob events are implementation details of the behavior and probably should not be exposed in /summon alone, or a distinction should be made between creation events and lifetime events.
Linked issues
is duplicated by 10
MCPE-86744
Piglins that have been given spawn events have broken ai
Resolved
MCPE-114874
Named pillagers will not attack the player
Resolved
MCPE-115868
Summoned piglin will not trade.
Resolved
MCPE-116722
Zombified Villagers that were Spawned in Using an Invalid Spawn Event do not Sit in Minecarts
Resolved
MCPE-119202
Fast Husk when born as minecraft:as_adult
Resolved
relates to 5
MCPE-76643
Rabbits Spawned with Spawn Event String Are About 2x Normal Size
Resolved
MCPE-116971
Patrol/illager captains don't attack when spawned by commands
Resolved
MCPE-140111
Cannot mount summoned horse with saddle
Resolved
MCPE-179414
Wolf summoned with tags cannot be tamed.
Resolved
MCPE-50328
Summon command gives speedy zombies & husks
Resolved
Comments 5
The addition of the /event command has mostly remedied this issue, since you can run initialization on the mobs after spawning them. However, it's still possible to violate the intended state combinations, like making a mob that's both an adult and baby simultaneously, and some of these are irreversible.
The official entity events documentation now fully explains this issue under the section "Strange Entity States Are Possible", here: https://learn.microsoft.com/en-us/minecraft/creator/documents/entityevents. At the end of this section there is a note that, to me, seems to say this is not considered a bug because using non-vanilla spawn events in commands is not supported:
These strange conditions of entities can be very entertaining, because they're unexpected, they also aren't intentionally supported. It's possible the specific behaviors of these odd states will change from one game version to the next as other intentional behavior is adjusted for new features or for bug fixing.
tryashtar
Confirmed in 1.16.100.55/1.16.40 hotfix. If i summon a pillager with the incorrect entity tag, the pillager never attacks the player, even when provoked.