Solution : https://service.sap.com/sap/support/notes/170679 (SAP Service marketplace login required)
Key words : 
additional key words, attached advance corrections, current exchange rate, billing split occurs, payment clearing item, payment clearing, billing split, invoice split, exchange rates, accounting rate
Related Notes : 
       
| 164422 | Billing item t.b. cleared with fixed exch. rate | 
| 150893 | Down payment clearing with separate exchange rate | 
| 113347 | Down payment process. as of Release 4.0x (standard) |