Yes, this has always been a royal pain. It's been this way for so long I've pretty much accepted it.
Most times I can send buyer a combined invoice (very easy for my auctions), but not so easy with Buy it Now items. As flipistics mentions takes a little more tweaking when combining Expedited Lite Packages since it automatically puts it into a new weight category. I can undertand that the system doesn't know the weight of the packaging and therefore that is usually the difference but as far as I know there is no way around it with calculated shipping be used.
It may be something else in your case though since you have a high feedback score, you have been here a while so I'm wondering if maybe something switched for you when they did a recent revamp to Business Policies. I know I had taken a few months off and when I listed this month my policies had changed in appearance, as well as where to find them within new listings. Something is different within the last few months with policies. The combined shipping bit has been wonky for me for many years now. It was great the first few years selling here, this was also back when everything was in US dollars, and everything went through PayPal but since the change over it's never been the same.
