Solution : https://service.sap.com/sap/support/notes/81121 (SAP Service marketplace login required)
Key words : 
additional key words co40, attached source code corrections, form routine comp_quantity_update, base units, production units, material master, finished product, production quantity, planned order, production order
Related Notes : 
       
| 174538 | CO40: Incorrect order quantities in collective order | 
| 117231 | CO40,41:Roundng error f.altern.header unit of meas. | 
| 78687 | Wrong component qty when converting planned orders |