Yip, they ensure that they get the biggest planes on the routes for this weekend. They also don't generally allow reward redemptions for Chuseok or Lunar New Year. Even Asiana blocks it all out for these times so no mater how many miles you have you can't fly them. Luckily I'm booked on their *A partner Thai. Good luck with the bus. Remember, if all else fails, take the subway to Seoul station and get on the airport express. It stops at Gimpo too.