To complete the story, it was indeed a mistake and AAdvantage fixed it. It was a pain to get there, as expected. First the agent didn't believe me that it originally was a P fare, but insisted it was O. Then they acknowledged it but only fixed one of the flights. Then, after calling in again and repeating the whole exercise, they now switched the complete flight to P fare, including two domestic legs which don't even offer PE. I'll leave it like that, not a big difference but I'll take it.
Thanks for the advice!