The card that I'd been using for my premium subscription was cancelled by the bank, due to the Target breach. I received a new card, and want to update my payment information. However, when I enter the card number the form moves me out of the CC number line once I reach 15 characters, instead of 16. Of course, this means that the card validation would not work because Visa accounts are 16 digits.
Eventually I was able to force it to accept 16 digits by clicking back into the CC number field 5 times and typing the last digit. However, I thought that you should be aware of this error because not everyone is going to be as desperate as me to get their premium subscription working.
FYI, I experienced the same error using IE, Chrome, and Firefox.