Sales order with no shipment created get a carrier number

hi Everyone,

In JDE 9.1, we are using transportation module for outbound shipments.

we recently have the issue that sales orders that do not have a shipment number (not commitment available) automatically get a carrier number which is the same for all orders, even if that carrier cannot be used for that customer/destination.

I checked customer address book and no carrier is entered there. Which setup or preference would attribute a carrier number to a backordered SO line?

Thanks

Nicolas