Solution : https://service.sap.com/sap/support/notes/758362 (SAP Service marketplace login required)
Key words : 
abap call interface, data arrives, incorrect format, /download reason, browser sends, multibyte format, automatic conversion, data provider, wrong format, explicitly converted
Related Notes : 
       
| 563161 | SAP GUI, SAP ITS & SAP IGS patches on Service Marketplace | 
| 335521 | ITS patch installation of kernel files | 
| 330793 | Downloading patches |