How can we improve WHMCS?

Currently when a client adds a new default credit card, existing invoices are not updated to pull from the new card. When the old invoice runs, it will attempt to charge the old default card (whatever was set when the invoice was created). This is very confusing for clients and there is no reason for them to expect this functionality.

When the client adds a new card and selects it as default, they expect that any charge run after that date will be charged on the new card. This is very important as it reflects badly on my business, causes extra work and irritates customers.