Solution : https://service.sap.com/sap/support/notes/351391 (SAP Service marketplace login required)
Key words : 
additional key words billing plan, attached source code corrections, payment condition azwr, pricing error vh810, takes inactive conditions, billing plan, partial billing, billing document, pricing error, inactive conditions
Related Notes : 
       
| 380675 | Statistical conditions in down payment items (2) | 
| 174608 | Statistical conditions in down payment items (1) | 
| 113347 | Down payment process. as of Release 4.0x (standard) |