When an item is not received eBay perceives that as a poor buyer experience and issues the seller a defect. Even if you issue a full refund without having a case opened you will still receive a defect. eBay will not remove it.
Although you don't have control over lost mail it is still your responsibility to get the product to the buyer. Tracking offers protection for lost items but, with the high cost, is not feasible for lower priced items. Therefore you have to eat the cost of those items that do not arrive.
In my opinion, giving a full refund is good service but eBay doesn't see it that way. I have received a few defects myself for INR and instant refund given. Therefore I try to get the buyer to wait a little longer before issuing a refund. If they receive the item and then re-pay you the defect will not be removed.