I don't know whether this is a deliberate choice in what matchmaking allows, but I just tied with someone in an open tournament on round two and then got matched with them again for round three. I know the matchmaking is based on placement (presumably to allow players who lost earlier rounds to catch up by forcing someone in a good position to lose), but I think an exception should be made for players who have already faced each other in that tournament. They already know each other's cards, and it's just less fun to go up against the same person twice when it could be a different person every time.