Solution : https://service.sap.com/sap/support/notes/421200 (SAP Service marketplace login required)
Key words : 
apocf010 sales order inbound processing, find sample source code, cross-system stock transfer, cross-system reason, individual customer basis, cif user exit, fill it_sl_doc-logsys, sales order item, purchase order item, assigned release order
Related Notes : 
       
| 603473 | Stock transfer -> release order is not deleted in APO | 
| 515499 | Release restrictions for R/3 Plug-In 2002.1 | 
| 515019 | Stock transfer -> incorrect/no release order deleted |