Solution : https://service.sap.com/sap/support/notes/434693 (SAP Service marketplace login required)
Key words : 
incorrect basic dates, order start date, order finish date, -house production time, basic date determination, capacity requirements determination, attached advance correction, material requirements planning, lead time scheduling, 'lead time scheduling
Related Notes : 
       
| 640207 | MD03, MD43: Incorrect planned order dates | 
| 603487 | Matl reqmts planning: No switching to forward scheduling | 
| 534380 | No adjustment of order finish date after lead time schedulng | 
| 441506 | Corr. to Note 434693: Reduction during lead time scheduling | 
| 406650 | No reduction during lead time scheduling |