Newbie ZIP code database mistake ... see if you can guess what it is

So, what happens when you put a novice in charge of defining your database schema? You get ZIP codes (really, postal codes) defined as integers. And what do you think happens when a downtstream consumer gets the data (formatted as a string)? CT starts looking a lot like MN, or some other place whose ZIP code doesn't start with a zero.

Oh, and they propagated this error all the way up through their outwardly-facing interface, too. I guess I'm just glad we don't have any Canadian or European customers.