Why are my invoices no longer organizing by number when recording a payment?

When recording a customer payment for multiple invoices, I have always clicked the invoice header in Record Payments. This has put my invoices in numeric order. Now when I try to organize them that way, clicking the invoice header just changes the direction the invoices are going, it does not put them in numberic order. Our invoices only contain numbers, this has only been a more recent problem, is there a fix to this or a bug that is causing them to not organize by which header I click on?