Recently a customer of ours selling large volumes of chocolate found that once an order's total weight reached the maximum shipping weight of UPS -- the shipping calculation went nuts. Since the shipment would not be one large box, but actually several smaller boxes this caused obvious problems.
We resolved this by splitting the total weight and calculating the shipping as separate containers. This is an option you can now control in your shipping settings.
Contact support@websiteforge.com with any questions about large shipments or split shipments. (over 70 lbs, over 150 lbs, etc. )