Bug mimic egg item isn't removed from inventory count when you fight the last monster in it

[Malibu Stacey]

Steps to reproduce:

1. Get a mimic egg which contains one or more monsters.
2. ash item_amount($item[mimic egg]) will return 1 as expected.
3. Fight all the monsters contained in your mimic egg.
4. ash item_amount($item[mimic egg]) will still return 1 but it doesn't exist any more in your inventory.