Similar issue with AF: can't change seats after having selected them when I bought my ticket. It's an AF ticket for an entirely AF-operated itinerary purchased through AF's website (FLR-CDG-JFK / SFO-CDG-FLR). I can see the ticket details online, but I cannot change any of the seats I chose for the long-haul flights in AF's website. I can change the seats for one of the legs (CDG-JFK) in KL's website, though.