Why won't a purchase order generate when running R31410?

Executing Outside Operations and the *Op item number is created, the router requires a purchase order, the vendor is defined and the cost type is set to D1.  The Supplier/Item relationship is created with the item restriction set up in the vendor master.

We're not seeing an error.  When we create the WO and attach the router using R31410, the router attaches but the PO is not created and the system states 'No PO'.