When entering shipping by quantity, I have set up my carriers beforehand, and I'm putting in the quantities. However, if I select a different shipping method (for example, UPS instead of Parcel Post), put in my quantities, and my shipping amount, it doesn't put the carrier into the grid below; instead it puts in the "Parcel Post" carrier.
I can go back and edit the lines in the grid afterwards, and tell it UPS, but it should get that from the form I'm filling in above, where I'm putting in quantity and amount.