3rd Party Sales- PR

Dear friends,

In SAP Library it is mentioned that u201CWhen you save a 3rd party sales order, the system automatically creates a PR. During the creation of PR, the system automatically determines a vendor.u201D But when I created a 3rd party Sales Order, PR was automatically created but no vendor was picked in the line item tab Source of supply (all fields in that tab were empty). Now my Question is that why any vendor has been picked in PR thru 3rd party Sales Order?

Kindly help.

Thank you