Mobs with multiple states have their hitboxs shifted when they spawn (except for the first state).
See examples for more infos.
- Activate hitboxes with F3+B
- Spawn a mob (like a Magma Cube or a Slime or a Pufferfish) and look at the hixbox of the mob
This bug occurs both when the mob appears with an spawn egg or a command (/summon).