Solution : https://service.sap.com/sap/support/notes/571786 (SAP Service marketplace login required)
Key words : 
customer-specific condition tables, assign data element kzfme, current purchase order item, purchase order item, product quantity processing, attached program corrections, transfer structure komp, expand structure komp, field ekpo-kzfme, price determination solution
Related Notes : 
       
| 817589 | ME59: Wrong net price when Requisition item has a batch | 
| 568209 | Pricing not considering batch specific conversion factors. | 
| 549013 | Wrong valuation at GR when using batches | 
| 490331 | Wrong valuation at GR when batch specific units of measure | 
| 390242 | Conversion factors are not determined for batch | 
| 162925 | Documentation for product quantity management |