I had an intriguing experience this weekend.
Being a 75K I had selected 3 Preferred seats together for myself, Mrs Nest (who is also 50K) and my child, who at 6'4" and 240lb could do with the extra legroom.
After online check-in I immediately got notification that my seat had been changed to the row behind (a non-preferred seat). When I went to change my seat back it was showing as unavailable.
I called to speak to an agent, who told me there was nothing she could do as the system was locked and only someone at the airport could give me my seat with my family back.

At the airport the agent said there was nothing they could do. Apparently the person that took my seat had paid for it, whereas I had selected it for free as a benefit of having 75K status.
And consequently they could not move that person out of their selected seat without asking their permission because they had paid for it. But they had no issue moving me out of the seat without consultation.
The manager I then spoke with was equally obtuse and uncaring, saying too bad, cash trumps status.

Eventually the situation was resolved when I was in the MLL. But it is concerning that AC will happily sell an already reserved Preferred seat if someone at check-in wants to pay cash. Benefits of status are apparently pushed aside.