Solution : https://service.sap.com/sap/support/notes/357628 (SAP Service marketplace login required)
Key words : 
incorrect main item number, additional key words transaction, parameter check tab page, /sapapo/bop_update backorder processing, backorder processing results, backorder processing created, source code corrections, rule-based atp, backorder processing, /sapapo/bop
Related Notes : 
       
| 375193 | Backorder processing: Composite SAP note on posting | 
| 356755 | Incorr.transfer of results of APO backorder proc. |