OK this is weird... my AP "send money" list of credit cards now lists only two cards, even though I have about 10 cards registered with Amazon (and shown if I click "Add a credit card"). Neither of the cards that now shows is the one I want to use this month.

Has anyone seen anything similar? How can I use my preferred card again?

[EDIT: After editing the stored card and re-selecting the billing address, it appears in the list again. Weird.]