Slimes splitting even when `PreventSlimeSplit: true`

Summary

When fighting a slime with PreventSlimeSplit: true it appears to work! However, after some time, maybe reloading the chunk, some baby slimes appear with the display name of the boss! Luckly the drops are just slime balls, but can be confusing for the players on the server.

Steps to reproduce

Monster:
  Type: Slime
  Display: '<#FF7D20>&lOminous Ooze &r&8[&f<mob.hp>&7/&f<mob.mhp>&8]'
  Damage: 1
  Health: 5000
  Faction: boss
  DamageModifiers:
  - ENTITY_ATTACK 0.60
  - PROJECTILE 0.50
  - MAGIC 1
  # Stop farms
  - DROWNING 0
  - BLOCK_EXPLOSION 0
  - POISON 0
  - MAGIC 0
  - WITHER 0
  - FALLING_BLOCK 0
  - THORNS 0
  - LAVA 0
  - FIRE_TICK 0
  - FIRE 0
  - HOT_FLOOR 0
  - FALL 0
  - SUFFOCATION 0
  - CONTACT 0
  Options:
    PreventSunburn: true
    AlwaysShowName: true
    PreventOtherDrops: true
    PreventMobKillDrops: true
    MovementSpeed: 0.5
    Silent: true
    Glowing: false
    Despawn: false
    ShowHealth: false
    # Slime specific
    KnockbackResistance: 1
    PreventSlimeSplit: true
    Size: 3

Current behaviour

Randomly you will see baby slimes that are not meant to be there around the world. They have the display name of the boss. I have not programmed any random spawns if you were wondering.

Intended correct behaviour

There should be no baby slimes as I set PreventSlimeSplit: true