When creating several payments under an invoice, a subsequent payment would normally only require the balance outstanding to be paid.
However, recently if you create an invoice and make a part payment (or receipt) and then click “create and add another”, the balance due is still the total value and not the outstanding value. If you simply create the value and create another payment, it is correct.
I suspect (although I may be wrong) it is a database/timing error and calculations haven’t been made yet.
Subsequent payments on the same invoice using “… and add another” don’t act as (I would) expected.