A LOT Polish Airlines Boeing 787-800, registration SP-LRA performing flight LO-91 from Warsaw (Poland) to Beijing (China), was climbing out of Warsaw when the crew stopped the climb at FL100 reporting a problem with the air conditioning of the aircraft. The crew subsequently advised there appeared to be a problem with the sealing which prompted ATC to query whether they had all windows closed. The crew decided to return to Warsaw, dumped fuel and landed back in Warsaw about 70 minutes after departure. The aircraft was able to depart again after about two hours on the ground and is currently estimated to reach Beijing with a delay of about 3 hours.