Updating loan's rate

[Old Philippe Debrabant]

Hi,

I always had problems with loan updating. At this time I have 4 loans in 
a file and each month, I have to manually update the repaid capital and 
the interest because the loans rates have changed some times ago.

I use the 4.8.0 version under Linux Mint 18.3 Cinnamon 64 bits.

Today I have to change the loan's rate of another loan and one more time 
KMM don't want to handle it correctly. But maybe I don't do the right 
thing ? Can I ask your opinion ?

Loan properties :
- the initial amount was 83531,60 €.
- on 28/02/2018, the actual due amount is 56520,00 €,
- the rate is 1,230 % for a year,
- amortization + interest are 534,42 € each month.
- on 10/02/2018 there are 113 payments left.
2 operations are registered in the account after 31/12/2018 : 31/01/2018 
and 28/02/2018.

On 01/01/2018, the rate change and become 0,890 % for a year. 
Amortization + interest are now 525,94 €. I need to change the loan 
properties and I cross my fingers.

Attention : I use the french translation, so the texts can be different 
from the real english translation

So I edit the account :
- select "modify loan's rate", next
- enter the date : 01/01/2018, next
- variable loan's rate, next
- next change of the loan's rate ? (No idea, it's the bank's decision. 
Why this question is asked). I don't change default values = 10/02/2018 
/ 1 year, next
- amortization and interests : I change 534,42 for 525,94, next
- Loan's rate : I enter 0,890, next
- Message : "KMyMoney has calculated 169 months as the term of your 
loan. The last payment was changed to 24.49."

It's a joke ???? Before the change there were only 113 payments left 
(after january) and now 169 ?
I check the january operation's repartition : amortization = 579,81 and 
interests = 58,91. On the bank side, the real term shows : 528,71 and 42,62.

SECOND TRY
I enter 525,94 (amortization + interests) and delete the loan's rate : I 
ask KMM to calculate.
Message : "KMyMoney has calculated 158 months as the duration of your 
loan. The last payment was changed to 433.08."
A new joke : 158 payments left ? Good job KMM !!!
On the confirm window, KMM display 0,000% as the loan's rate. Bravo !

THIRD TRY
I delete the amortization and enter the new interest amount : 0,890 : I 
ask KMM to calculate.
Error message : "You have entered incorrect information. Please go back 
to the appropriate page and update the numbers or leave a blank value to 
let KMyMoney calculate it for you".

I think it's no possible to change the loan's rate.
An idea ?