Solution : https://service.sap.com/sap/support/notes/46493 (SAP Service marketplace login required)
Key words : 
additional key words me21, prerequisites solution corrected, -party order, sales order, delivery address, po created, created manually, -party processing, advance correction, source code
Related Notes : 
       
| 204190 | Third-party: No update of purchase order with SP change | 
| 38977 |