Shipping cost is calculating wrong for International orders

I have noticed a disturbing problem over the last few weeks. Several International orders, both Priority and Express Mail, are calculating way too high. Our customers have pointed this out, and now I notice it happening more and more. I know that it is not a weight issue because the package weight is correct.

after the first time this happened, the order had been fulfilled and sent. I opened a case with Netsuite and their response was to send me links to information about all the different things that can affect shipping costs. I understand there are many factors in determining shipping costs, but when all the parameters in NS are correct (shipping weight and dimensions, shipping method, insured amount, country...) the shipping amount should be correct also. Finally I was told that 2 packages had been sent out, but I could easily see in the Related Records field that was not the case.