Solution : https://service.sap.com/sap/support/notes/138502 (SAP Service marketplace login required)
Key words : 
additional key words message number, product number conversion, oltp - material master, incorrect data storage, apo - product master, create report zprodnradjust, source code corrections, source code, longer display, /sapapo/mat1
Related Notes : 
       
| 168128 | Numeric product number: Correction for 138502 | 
| 138510 | Creating, changing, displaying product not possible | 
| 138372 | Aligning APO Datamart, and APO for Product Number |