Solution : https://service.sap.com/sap/support/notes/529838 (SAP Service marketplace login required)
Key words : 
system generates incorrect confirmed dependent requirements quantities, prerequisites program error/program design, availability checked planned orders, material requirements planning, planned order processing, active simple discontinuation, succession requirements, program corrections, dependent item, planned order
Related Notes : 
       
| 622524 | Plnd. order: Confirmed quantities for discontinuation items | 
| 538634 | |
| 534269 | Conversn of plannd ordr and discontintn: Incorrct ATP reslts | 
| 525272 | |
| 522044 | Discontinued part: Confirmed dependent requiremts quantities |