Solution : https://service.sap.com/sap/support/notes/543203 (SAP Service marketplace login required)
Key words : 
rule-based availability check, title program lcavef15 category, apo backorder processing, source code corrections, data type 'cif_sl_hx', backorder processing remains ', apo outbound queue, include program status, productive save application, early confirmation transferred
Related Notes : 
       
| 546879 | BOP: Error during the R/3 update | 
| 542191 | Processing rejected items | 
| 375193 | Backorder processing: Composite SAP note on posting |