Solution : https://service.sap.com/sap/support/notes/640207 (SAP Service marketplace login required)
Key words : 
generate incorrect basic dates, displayed basic dates correspond, replenishment lead time, lead time scheduling, backward scheduling activated, -house production times, attached program corrections, punctual requirements coverage, basic dates, basic scheduling
Related Notes : 
       
| 603487 | Matl reqmts planning: No switching to forward scheduling | 
| 534380 | No adjustment of order finish date after lead time schedulng | 
| 503991 | Planned orders are moved into the planning time fence | 
| 441506 | Corr. to Note 434693: Reduction during lead time scheduling | 
| 434693 | Correctn for Note 406650: Reduction for lead time scheduling | 
| 406650 | No reduction during lead time scheduling | 
| 207572 | MRP: Plnd orders w/ basic start > basic finish |