Solution : https://service.sap.com/sap/support/notes/385810 (SAP Service marketplace login required)
Key words : 
additional key words transaction, entries remain hanging, source code corrections, subsequent order items, /sapapo/bop_updatebackorder processing, order item, backorder processing, /sapapo/bop, /sapapo/bopi, partially updated
Related Notes : 
       
| 420605 | Composite SAP Note for BOP performance in APO 3.0A | 
| 375193 | Backorder processing: Composite SAP note on posting |