Solution : https://service.sap.com/sap/support/notes/380431 (SAP Service marketplace login required)
Key words : 
additional key words transactions, attached source code corrections, completely update order items, symptom order items, /sapapo/bop_updatebackorder processing, order item, backorder processing, /sapapo/bop, /sapapo/bop_worklist, /sapapo/bop_result
Related Notes : 
       
| 420605 | Composite SAP Note for BOP performance in APO 3.0A | 
| 375193 | Backorder processing: Composite SAP note on posting |