Credit Card Numbers Missing from Order

[IncrediBody.com]

I received a an order that says Payment method: credit card. It has all the shipping and billing information and what was ordered. They only problem is it does not have any credit card information in Zencart. The e-mail I receive with the middle digits just says Middle Digits: and then is blank. I have received credit card orders both before and after this specific order and they have come through fine. I am running Zencart 1.3.6. Does anybody have any idea what might have happened to this specific order?

[IncrediBody.com]

As an update to this, the customer just informed me that he got an error page instead of the order confirmation page. Do you think this was just a freak occurence, and nothing to worry about?