Solution : https://service.sap.com/sap/support/notes/500500 (SAP Service marketplace login required)
Key words : 
original confirmed schedule line, apo backorder processing, desired delivery time, confirmed time, prerequisites actime, solution note 494270, confirmation, determined, prerequisite
Related Notes : 
       
| 494284 | Backorder processing: R/3 ACTIME | 
| 375193 | Backorder processing: Composite SAP note on posting |