Additional Shipment on Shipped Order Miscalculation

[iloveitaly]

1. User completes order
2. Order is shipped
3. User wants to add an additional item to the order which needs to be shipped in a separate package
4. New shipment is added via the admin order shipments area
5. Shipping cost is calculated based off of line_items and not the unshipped inventory items

Possible solution:

1. In packages check if the order is complete
2. If the order is not complete, use line_items to calculate shipping
3. Check if the order's shipment is shipped
4. If the order is shipped, calculate the shipping cost based on the inventory units that are not shipped

Of course store preferences for inventory tracking will have to be taken into account.