Solution : https://service.sap.com/sap/support/notes/504124 (SAP Service marketplace login required)
Key words : 
possible534944 ratenberechnung bei vorgabe aller raten536093 payment plan creation method, 10_05 requires sab_aba support-package level sapka50a10, mengensplit nach floating rate anpassung539462 add, contract start date invalid528276 change processes, serial number527423 change financing amount, partner changes528343 payment schedule, rate/x527530 incorrect customizing, due dates513399 date duration, installments/shortened period/end, crm document504148 incorrect calc
Related Notes : 
       
| 567207 | |
| 565970 | |
| 559364 | |
| 540918 | |
| 539462 | |
| 534944 | |
| 531400 | |
| 529817 | |
| 529656 | |
| 528343 | |
| 528276 | |
| 528170 | |
| 528169 | |
| 527560 | |
| 527530 | |
| 527423 | |
| 527003 | |
| 524041 | |
| 523432 | |
| 523408 | |
| 522783 | |
| 521003 | |
| 519713 | |
| 518262 | |
| 517651 | Actions: short dump when navigating or saving | 
| 513399 | |
| 512153 | |
| 507302 | |
| 506668 | GRID_CHANGED event is not sufficiently transparent | 
| 505536 | XIF business transaction: inbound error on item level | 
| 504148 | |
| 499375 | Endless loop when changing a CRM document | 
| 456853 | Change indicator is set | 
| 449055 |