I was upgraded at 4 days out for a flight on a 757, and logged in and switched my assigned seat to 1A. I know it took because it was there the next day. When I logged in today to select a seat for my return leg, I noticed I had been switched out to 6A. I am still in first, so I can live with this, but does anyone know why they would just switch me out? Should I not bother trying to snag 1A?