Method to disable adding 1 to product inventory when product is deleted from customer's account

We lease-to-own products (computer hardware), using WHMCS as our shopping cart, client area and monthly billing system.

After so many payments, a customer purchases the product and we then delete the product from the customer's account.

HOWEVER, when we delete the product, WHMCS automatically ADDs 1 to that product's inventory (yet we don't actually have one in stock).

Proposed Solution: Provide capability to disable this feature by product.

Thanks for your help and consideration,

James