Solution : https://service.sap.com/sap/support/notes/493568 (SAP Service marketplace login required)
Key words : 
attached source code corrections, changed sales order items, oltp sales document, connected oltp system, oltp system, backorder processing, terms transactions, /sapapo/bop, /sapapo/bop_update, /sapapo/bopiupdate
Related Notes : 
       
| 497590 | Backorder processing: update status not set | 
| 375193 | Backorder processing: Composite SAP note on posting |