Spawn eggs with custom nbt may occasionally naturally spawn a passenger. For example, a Strider may occasionally spawn with a baby Strider or Zombified Piglin riding it when using a custom spawn egg for striders. The same data when used in /summon or a spawner will not spawn the natural passenger on top. This happens with all entities that can have natural passengers, including spiders and chickens. This bug relates to MC-85340 but is different in that it does not involve setting the passenger tag itself.

Expected behavior:

Spawn eggs with custom nbt should never spawn natural passengers as this behavior is inconsistent with /summon and spawner behavior. This also makes it impossible to guarantee a spawn egg will spawn the same entity on every use (as there is no way to control the natural passenger).

To Reproduce:

1. Run the following command to give yourself a custom spawn egg with custom NBT.

/give @p minecraft:strider_spawn_egg{EntityTag:{CustomName:'"example"'}}

2. Use this spawn egg several times and observe that sometimes baby Striders or Zombified Piglins will spawn on top of the strider.

3. Run the following command several times and observe that the custom NBT restricts the strider from naturally spawning a passenger entity

/summon strider ~ ~ ~ {CustomName:'"example"'}

4. Another example of expected behavior is via a spawner.

/setblock ~ ~1 ~ spawner{SpawnData:{id:strider,CustomName:'"example"' replace}}