Solution : https://service.sap.com/sap/support/notes/170088 (SAP Service marketplace login required)
Key words : 
additional key words co01, variable-size item quantity, variable-size item, variable-sized items, requirement quantity, calculated correctly, production order, implement note 108300, phantom assembly, incorrect quantities
Related Notes : 
       
| 108300 | Incor.size quantities after change i. qty i. header | 
| 73033 | Component quantity in production orders |