[1.16.5] saving tags to item via event interactLivingEntity not working in creative

I'm trying to overcome a little issue.  I'm trying to save data to an item's tag.  This works perfectly fine in survival but does not work in creative mode.  

 @Override
    public ActionResultType interactLivingEntity(ItemStack stack, PlayerEntity player, LivingEntity livingEntity, Hand hand) {
        if (hasAnimal(stack) || !livingEntity.isAlive() || livingEntity instanceof PlayerEntity) return ActionResultType.PASS;
        if (!player.level.isClientSide && livingEntity.isAlive() && livingEntity instanceof MonsterEntity) {
				CompoundNBT entityNBT = livingEntity.serializeNBT();
                stack.getOrCreateTag().put(NBT_ANIMAL,entityNBT);
				livingEntity.remove();
                return ActionResultType.SUCCESS;
		}
		return ActionResultType.PASS;
   }

I totally get if I was trying to do something like ItemStack.HurtAndBreak()  which would damage it, but the tags don't even populate with data once outside of this event (They are retrievable while still locally in the event and have access to the instance passed into the event).

The item in question is a single-stack item.

Switching to Survival rectifies this situation.

Is this expected? Normal?  If not am I doing something wrong?  

~BrewingCoder