The shipping tables need to additionally filter by TabID. With multiple instances of the cart, (either on separate Tab or on another portal) the TabModuleID is not passed to the SP.

Therefore, if you select "Shipping by Quantity" on more than one cart, all of the other shipping by quantity information bleeds over.

So, the problem that presents for ME is, I'm trying to figure out the best way to ship to the UK, because of the following issues:

1) UPS Ship Calculator errors on UK addresses.

2) UPS is EXPENSIVE to ship to the UK.

3) You can't have both "UPS" and "USPS", without building a custom ship methods table

4) Since one store ships very small items, and the shipping by quantity is set up for that, I can't create (on another tab or portal) shipping by quantity for another product.