Solution : https://service.sap.com/sap/support/notes/400517 (SAP Service marketplace login required)
Key words : 
additional key words transaction, attached source code corrections, individual documents hang, prerequisites solution implement, material availability date, /sapapo/bop_updatebackorder processing, backorder processing, delivery date, /sapapo/bop, /sapapo/bop_result
Related Notes : 
       
| 402505 | Backorder processing: Loading date not taken into account | 
| 375193 | Backorder processing: Composite SAP note on posting | 
| 372123 | Backorder processing: Update is incomplete | 
| 371840 | Backorder processing: Scheduling with groupings | 
| 332401 | Backorder processing: Result transfer, value addition |