Just had an error happpen to me. I usually print the invoice once it is sent but got an error when I clicked on view Order Details straight after sending the combined invoice. I finally got to the Order details by going to my Sold list. I also noticed that the postage is again showing in US dollars. Hope it shows correctly for the buyer.

I just sent a combined invoice to a buyer, who bought 2 items, both with $8 postage. Instead of charging $16, I charged $8, as you do. I just checked the order details and it's saying $US16 for postage! I checked the invoice that CC'd to my inbox and it says $8 postage, so hopefully all is good!