USPS Shipping Sometimes Left Out of Order

Hi All, here is a quick minor problem I have. I was wondering if anybody else has had this happen to them.

The client who manages all the orders noticed a few orders slipping by without shipping charges added to the total. I checked the data in the DB and found that for those to order, the post content serialized data was missing this:

s:19:"shipping_sub_option";s:23:"First-Class Mail Parcel";

Now I really think this might be more of a USPS API being down type of deal, but I just wanted to bring it up here in case anyone else had similar issues.

All other orders have been correctly processed.