Most likely, this has NOTHING to do with Mr United.com. It has to do with how some of the Star Alliance handles reservations. When you are making "reservations", you are fundamentally making a request for a seat. Most US carriers have immediate confirmation, thereby granting your request on the spot. Other carriers allow the requests to queue and grant requests at specific times (say, overnight). Finally, some carriers may still manually be granting requests (a live person touches the reservation).