I've had a related experience. I have permament residency and a valid DNI. I fly round trip from Argentina to the US 8 - 10 times per year, have been for the last 4 years, always on American Airlines. A few times I've had AA staff ask me why I was flying one-way to Argentina when I was checking in, I simply said I live here and have residency and that was the end of it. But for the first time this past summer I was flying out of Boston when the agent demanded to see my DNI. I showed it to her, of course she couldn't really read Spanish so she made a mess of interpreting it. I tried to explain to her what the various data fields meant, but she didn't trust me. She wanted to know why there was no expiration date, and she was suspicious simply becuase DNIs contain lots of hand-written data. I asked her to get her manager, but he never showed up. I asked her for her name, and to see her employee badge, she refused. I asked her to call someone for help, I know the airlines have internal helpdesks set up for just this sort of situation, where someone familiar iwth the weird documentation from some oddball country can walk the agent through interpreting a passport or ID. After more than 30 minutes of her petty refusal to get help and let me proceed another agent took the DNI from her, spent 10 seconds examining it, and told her "He's right, he's a permament resident, why don't you give him his boarding pass?!?!" I reported my experience to American Airlines customer service, they acknowledged my report with great concern but never told me what, if anything, they did about the original agent's behavior and apparent lack of training.