A review pass on our credit calculator flagged something that should have been impossible: a

finding tagged HIGH, on a panel with a full test suite, where every individual test passed and

the answer was still wrong. Not "wrong in an edge case" wrong. Wrong for every single user who had

ever configured a Sondertilgung (a lump-sum extra payment on their mortgage) and then looked at

the "what if I invest the difference instead" comparison next to it.