Well technically speaking, they actually have to reverse beyond the station, because Lewes has 5 platforms, 3 for the Coastway line to Brighton, and 2 for the Mainline to Brighton. Technically speaking, that would mean when departing from Brighton, you could legally be in declassified first class, but when the train reached its first calling point at Lewes, it would now be classified as first class under their rules and issue you a penalty fare as you are now in the front first class, and that is only if they choose to call at Lewes, since as they cant reverse in the station, they could easily then pass through the station without stopping again only minutes before or after the stop at a junction to reverse the train, meaning the first calling point would be Wivelsfield or Haywards Heath, although that does give plenty of time for people who were sitting in first class to both swap ends.