Originally Posted by
Pickles
What the agent should have done is scanned your US passport, not your foreign passport. As a US citizen you are supposed to leave on your US passport. What you use to enter the other country, the US doesn't care as much, and showing (but not letting the agent scan) your foreign passport would have been sufficient for the agent to issue you a BP.
To enter your home country, you could have used either, although your home country passport is probably less of a hassle in terms of lines, etc. And, of course, your country may have similar regulations to those of the US, in which case you have to enter with your home country's passport.
In the end, I don't think it will be a big deal, when you re-enter the US you will certainly use your US passport.
Agreed. You could ask the TA to swipe your US passport to authorize your departure from the country, and then show your foreign passport to document that you can enter the host country.
In fact, it could cause problems for you on the return if you depart the USA on a non-US passport and try to re-enter on a US passport. All of your departures and arrivals (by air) show up on the passport control officer's screen, and if you are re-entering without showing a departure, you might get sent to secondary for some questioning.
It happened to a friend of mine who went by land into Mexico and then flew back. The CBP computer didn't have a record of his departure, so he was detained briefly while he explained how he had left the country without having his passport swiped.