item lock = byebye item?

It's not that Nexon transfers the expiration date, it's just that they forget to remove it. That's why expiring items can't be locked: because the item-lock uses the same expiring-date attribute. Whenever the lock is applied, an expiring-date will be set on that value, and a lock-attribute is placed on the item. The item will expire normally when the lock-attribute is off, and the lock will expire whenever the lock-attribute is on. Then the date is removed. Guess what happens when the date is not removed.