Solution : https://service.sap.com/sap/support/notes/115380 (SAP Service marketplace login required)
Key words : 
--> command line ' check cm61o-noavm ne xflag, repetitive manufacturing planning table, additional key words mf50, 10 1 pc = 10 pcsthis proportional adjustment, change structure cm61o, detail dialog box, attached section 'programs -, field 'ptmod no_prop_scrap', form routine comp_ausschuss, expand structure cm610
Related Notes : 
       
| 855524 | MF50: incorrect scrap qty in planned orders | 
| 115871 | MF50: Rounding error |