redshift
LE
German by birth, British by adoption and marriage, and now a septic. Makes for a fun time at passport control, Germans get really stroppy if I try to go in on anything other than a German passport. This time around I dropped all three on the counter for the Bundespolizei bloke, he smiled and said, "Ach, Jason Bourne. You only need to show your German passport Herr Effendi".
It is to do with immigration status. If I arrive on the German pass I can stay indefinately, if I arrive on the US pass I am limited and only have tourist rights to healthcare etc.
What happens when you enter the U.S.? Assuming you have to use the U.S. passport? I've never had anything else apart from the U.S., so don't know. Though, I will find out next year when I get a Brit one.