It is not possible for buyers to ask for combined invoice ("Request Total"), and not possible for sellers to issue such invoices. Possibly the glitch only affects international transactions.
When trying to ask for total, I (a buyer) get following error message:
"The seller doesn't offer combined postage discounts. Either the seller has disallowed combined payments and postage discounts, or the time period specified by the seller for combined payments has expired. Please proceed to checkout to complete your purchase."
This has already happened with 2 sellers who both allow combined payments (one of them wrote that he was also unable to issue combined invoice), both transactions were international.
