I created a loan with the following characteristics:
- loan amount : 20000 €
- interest rate : 2.32 %
- term : 6 years (72 months)
- payment (principal + interest) : 536.09 €
- fixed fees : 11.09 €
- periodical payment : 547.18 €
- first payment : 31/10/2012

I entered the 25 payments between 30/11/2012 and 31/10/2014.

Two years after the beginning, on the 01/11/2014, the interest rate change for 1.75 %. The number of terms is not modify, only the monthly payment is reduced.
I tried to change the interest rate with an applicable date of 01/11/2014, but the result is incomprehensible !
The date of the last payment operation entered is 31/10/2014. It remains 47 payments.

- Before the change, the amount of monthly payment is : 547.18 € (including 11.09 € of fixed fees).
- After the change, the amount is 541.40 € (always 11.09 € of fees).

This is what I tried :
1) Edit the account
2) Select Modify interest rate
3) Changes will be active on 01/11/2014
4) Variable interest rate (no change)
5) Next change of the interest rate on 01/11/2015
6) Principal and interest : 541.40 - 11.09 = 530.31 €
7) Interest rate : 1.75 % => popup : "KMyMoney calculated as 71 months duration for your loan. The last payment was changed to 284.38. Accept this or modify the loan information and recalculate." (google translation)

It's not correct, the number of payment shouldn't be recalculated (and enlarged).

But when I checked the next operation to enter (30/11/2014) the amounts are almost good : principal=495.22, interest=35.09 (fees=11.09) in place of 494.82 and 35.49.
So I tried another time to change the loan properties, but this time, I choice "modify another information". I change 71 months to 72 and clear the final payment value. The popup announced a final payment of 0. BUT CHANGE the first payment to 01/10/2012. If I checked the next operation, nothing has changed. The date is always 30/11/2014 and principal / interest : 492.22 / 35.09.
The behavior seems very weird and unpredictable if I compare to MS Money 2003 I used before.

Do I made an error somewhere ? How can I obtain the correct values 494.82 / 35.49 ?

I'd suggest you make a backup, and try deleting and recreating the loan with the updated principal and interest rate.

Thank you for your answer, but no, I prefer report the bug (for me it's a bug, not a feature). Changing an interest rate is an ordinary operation. It shouldn't be necessary to delete and recreate the account mostly for the "BEST Personal Finance Manager for FREE Users". MSMoney do that since a long time without effort.

Another point with the loan management, I made a exceptional payment for a loan. In that case I must have the choice to reduce the number of terms or reduce the amount of each payment. KMymoney seems not to deal with that no more. If I want to change anything it consider the initial values and not the current values. Thus, for that loan I created a new loan with the remaining amount and made a transfer to the old loan. Next I closed the old loan. With MSMoney, it was much simple, no need to close the first loan and create a new one.