Solution : https://service.sap.com/sap/support/notes/684212 (SAP Service marketplace login required)
Key words : 
symptom backorder processing incorrectly selects, interactive backorder processing reason, rules-based atp, source code corrections, delivered rba, erroneously created, customer order, solution implement, additional, prerequisites
Related Notes : 
       
| 375193 | Backorder processing: Composite SAP note on posting |