Solution : https://service.sap.com/sap/support/notes/495273 (SAP Service marketplace login required)
Key words : 
rules-based availability check disappear, data elementdelet                   cifschedvsmng                   vsmngthen change, data elementdelet                   bapiupdatevsmng                   bapiupdatesave, apo backorder processing, main item consists, request schedule lines, currency/quantity fields, symptom occurs, sourcing reason, program error
Related Notes : 
       
| 498795 | Backorder processing: Several request schedule lines | 
| 497172 | Backorder processing: several request schedule lines | 
| 493656 | Sales order items not updated in the OLTP system | 
| 375193 | Backorder processing: Composite SAP note on posting |