Maturity date calculation for future dated payments

Dear Community,

I want to create a future dated payment.

In Payment Method - I marked "Use Payment Method to Issue Bills Payable"

I have entered two invoices:

1) Standard invoices - amount 1,000,000 in Scheduled payments tab the due date - 15/12/2014

2) Credit Memo - amount -10 in Scheduled payments tab the due date - 02/12/2014

When I create a future payment for two invoices the Maturity date = 02/12/2014

The system always takes a Maturity date the earliest of the two invoices Scheduled payments

What is the logic for calculating Maturity date ?

thanks,

Alex