Solution : https://service.sap.com/sap/support/notes/79149 (SAP Service marketplace login required)
Key words : 
additional key words co01, order header / phantom assembly, source codeimplement notes 73033, phantom assembly, order quantity, production order, source code, component quantity, subordinate component, adapted accurately
Related Notes : 
       
| 308461 | Rounding error in quantities of alternative items | 
| 158411 | CO01,02:Incor. qties f.dirctly manufactrd component | 
| 117321 | CO01,02: Rounding error for component quantities | 
| 115011 | CK11: Usage probability for alternatives | 
| 112062 | CO01/02:Incor. phantm qties when changing headr qty | 
| 110734 | CO01: Requirement quantity of a size not rounded | 
| 101007 | Wrong qantty t.be dscntnud for header qantty change | 
| 93354 | Incorrect component qty when changing header qty | 
| 77187 | Computation of quantities for material components | 
| 73033 | Component quantity in production orders |