I have made a new payment term in order to manage the installment of my invoices: a 50% should be paid after 30 days and the remaining 50% after 60 days. Now, when I validate the invoice the accounting entries are generated correctly, however when I try to pay the invoice manually, the voucher expose the total amount instead of the 50%, and each time I need to correct it to register the partial payment.

Is there some option that I'm missing, or this is how it really works? 

(This is bad: Imagine to correct manually about 3000 invoices per mount...)

Thanks in advance to anyone who will find his time to reply! :)