Why does my freight term show YPA prepay and add?

The Customer Freight Policy for SI LP businesses is as follows:

Transportation costs will be covered by Siemens provided

• An order has a minimum net value of $1000
• The order ships within the Continental US
• Siemens selects the carrier

As long as the above criteria's are met, if the freight term on the order is YPA, the freight term on the shipment and invoice will be automatically changed to YPP Prepaid and Allow.