Solution : https://service.sap.com/sap/support/notes/437480 (SAP Service marketplace login required)
Key words : 
sap gui generate single-shift-2-control characters, sap guis sinf release 6, enterprise web application servers, ascii-based application server, 10-based front end program, ascii-based front end, ebcdic-based application server, transaction sends x'0a', rfc               transaction sends x'25', send rfc control codes
Related Notes : 
       
| 487923 | Undesired special charac. 6.10 GUI at AS/400 | 
| 410189 | Modification Assistant on platform with EBCDIC code faulty |