I ended up in the middle of something on a plane that was similar to this. The airline had changed the flight number in the middle of a flight and then landed at Phoenix, Arizona just long enough to drop me off (I was more or less told to grab my carry-on bag and run for it). I ran to the bathroom, and came out to hear my name being paged to report to Gate X for final boarding. I'd been in the airport less than 5 minutes total. So, I got to the plane, and was put in the seat that corresponded to my seat number on my ticket, which turned out to be next to a loud snorer until the next stop, in Los Angeles.
In Los Angeles, a woman gets onto the plane, stops in front of me, says, "You're in my seat," and thrusts her ticket in front of my nose. I got mine out, and because of the airline changing the flight number and the other gyrations I'd been through, she and I had the same seat number. I called for the stewardess, and she offered the lady a different seat. No, the lady was very insistent - she wanted the seat I was in because it was "hers." I ended up changed to an empty row (nice!) The ironic thing was, the lady wasn't traveling with the people who were next to her, so she got to sit next to the snorer all the way into Sacramento.