Incorrect fields when creating provider term

Hello,

i create provider term for provider bill and need to set 3 terms : 40%, 30 % and 30%.

Order to provider is 99 000 € on project expense of 100 000 €.
 

Project expense real amount is well corrected to 99 000 € as expected.
Provider bill is 99 000 € on provider bill 99 000 € as normal.
 

I want to create three terms as decribe above so i start with the first one (40%).
 

After creating term, bill amount is set to term amount, i can't create new term.
 

I need to reset bill amount to 99 000 € to be able to create second term.

And so for the third one.

Expected behavior : bill amount don't change (if i record a bill, i get the bill in my hands so it is real and can't be modified by ProjeQtOr).  Terms as to be set to reach the bill amount. It works fine if you set multiples terms with exact amount for each but for terms fixed in contract (so 40% on delivery, 30% on VA and 30% on VSR) how to set this ?

Regards