Solution : https://service.sap.com/sap/support/notes/390641 (SAP Service marketplace login required)
Key words : 
forward scheduling determines shorter lead times, net invoice determines order dates, additional key words md01, attached source code corrections, forward/ backward scheduling activated, lead time scheduling reduces, net invoice determines, incorrect planned order dates, determined order finish date, -house production times
Related Notes : 
       
| 489565 | MD05: Incorrect planned order dates in MRP list | 
| 359288 | Incor.available qntity for scheduled planned orders | 
| 207572 | MRP: Plnd orders w/ basic start > basic finish |