A customer would like to use the function “Customer Repayment Proposal” but it seems that the results become quite strange when advance payments are made to advance invoices. In these cases, 

when called using the option “Include Advance Payments” the proposal doesn’t include the payments but the respective invoices if those are not fully paid. This doesn’t make much sense in this context because what usually has to be repaid are just these payments (and payments on account), whereas an open advance invoice should not be used to reduce the repayment (what can happen with open amounts from regular invoices). 

Now, when an advance payment is registered just as customer payment in Mixed Payment with the “Advance Payment” box ticked, this advance payment then actually would appear in the repayment proposal! But this box is never ticked (and can’t be) when entering a payment against an advance invoice.

So, it seems that things don’t really fit together here, do they? Or do the customer and I misunderstand the purpose of this function?