Solution : https://service.sap.com/sap/support/notes/796000 (SAP Service marketplace login required)
Key words : 
terms /sapapo/dm_order_merge_opr, source code corrections, sap apo systems, deallocate operations, process orders, status scheduled, pi dummies, pi activities, schedule reason, program error
Related Notes : 
       
| 789946 | Adjusting secondary resources during confirmation of phases | 
| 370959 | Always schedule operations of R/3 orders |