Originally Posted by
CPS89
My seat was 9C when I last looked before boarding but became 15A when I was on the plane. Not sure I even had recourse with a paper BP, as PP is E+ on that flight.
Seat assignments are never guaranteed. However, employees are generally* not allowed to boot other passengers out of a seat assignment because
they'd prefer it. If you're certain that the people who took your seats were employees, I'd write to United to let them know -- something like, "FYI, I was on flight 1234 and I got removed from my preferred aisle seat after boarding and put back into a window seat. Although I realize that seat assignments are not guaranteed, I was very disappointed when I saw that I'd actually been re-seated to make room for United personnel."
That said, you're always going to be in better shape with a paper boarding pass, because you can show that you did have claim to that seat at one time. That's tougher to do with the electronic passes. If these people really were trying to pull a fast one, they may have been counting on you not being able to prove your point easily. (It's all in the computer, of course).
* Unless they've managed to negotiate it into their contracts. However, I find it hard to believe that UA would have specified a Premium Plus seat priority for flight attendants, especially if they really were off-duty (i.e, commuting, as opposed to deadheading).