How can prepayment amount to be deducted be manipulated?

FragenFrager

Hello,
one of our customers reported the following problem:
In an order for which two prepayment invoices (one for 90% and the other for 40%) have been posted, the prepayment amount to be deducted is different from the prepayment amount and is lower.
I looked at the lines for the order; 5 units of quantity of an article are entered in one line. The prepayment amount seems to refer to these 5 quantities, but the prepayment amount to be deducted only corresponds to one item (i.e. 1/5).
Unfortunately, I have absolutely no idea how this amount got there. According to the change log, this amount was initially put there and then no longer changed.
I tried to recreate the problem in a demo client as follows.
- Order created
- first prepayment invoice for 40% created.
- second prepayment invoice for 90% created.

Now when I try to enter a lower value in the Prepayment Amount to Deduct field, I get the error "Prepayment Amount to Deduct Excluding VAT cannot be less than the Invoiced Prepayment Amount Excluding VAT ."

Edit: A partial delivery was created for the order after the advance payment, but only for 1 item. Then the advance payment amount to be deducted will obviously also be reduced, I was able to do this in the demo client.
I think the tooltip is a bit misleading; He says it is the amount that is invoiced with a normal invoice. A normal invoice has not yet been invoiced.