Solution : https://service.sap.com/sap/support/notes/505757 (SAP Service marketplace login required)
Key words : 
system displays billing plans incorrectly, create billing documents, terms ff7b reason, attached advance corrections, billing plans, system considers, liquidity forecast, reduction correctly, display amounts, fi posting
Related Notes : 
       
| 506933 | Baseline date for payment for down payment dates from SD |