In the shipment cost document (VI01), What is the source of the plant code (VFKP-WERKS)?

When creating a shipment cost document (VI01), I am getting this error message, "Inconsistency between a document field and the prof. segment number." I can force the shipment cost document to create, however, it will not transfer. Drilling into the error message, I notice that the plant code in the shipping cost doc. (VFKP-WERKS) is different than the plant code in the originating document (e.g.1. plant code in purchase order is 1040, and the plant code in the shipping cost document is 1080); (e.g.2. plant code in sales order is 3130 and the plant code in the shipping cost document is 1040). Where does the shipping cost document get its plant code?