Why? We certainly didn't see every court case ever. And in a world that has spells like "Wingardium Leviosa", "Ascendio", or "Locomotor", I see no reason that the seats couldn't move around a bit. I can easily see things getting wonky real quick if they were to try to put a powerful magical werewolf, that by chance has some REALLY powerful witch and wizard friends, on trial for Murder. As a matter of fact, I would expect them too.
Perhaps this could be saved for the MoM thread; but would Harry, Ron and Hermonie be then as simply put; the bad guys in this situation?