I have been having the same issues, I rang eBay yesterday and they said I was set up correctly, but customers are saying they are not able to request total or combine an invoice, not happy with this as eBay stated that it must be the customer not worrying about postage costs,  I have a sneaky suspicion they want the higher costs because they take 11% from the postage costs as well as the item sold, so that can be a substantial amount when the postage has not been discounted by the seller. It is upsetting as it makes sellers look like they are ripping people off, I alway send free stuff to cover the extra post but should not have to do that, but at least customers seem to be happy with that for now 🙂