Solution : https://service.sap.com/sap/support/notes/156870 (SAP Service marketplace login required)
Key words : 
alpha conversion exit additional key words olap, blending purely numeric characteristic values, alphanumeric characteristic values results, '1a' --alpha--> 1a display, alpha conversion exit, conversion exit works, display characteristic values, --alpha--> '12'               ad case 2, business information warehouse, inserted left-aligned
Related Notes : 
       
| 447341 | values for ALPHA conversion routine |