What about the size of the door (space) and how long has it to be opened (time)?
I think Maxwell's demon would have a problem with space, if the door is too wide (more than one particle size), then direct interaction between the two part is possible and would lead to lose isolation restriction, like there were no demon, (even no isolation wall). On the other hand, if the door is too narrow, then no particle can go into or it will let pass only those which are direct aimed, then Maxwell's demon would lose its freedom of choice because the narrow gate itself "choose" particles having a direction perpendicular to the wall, despite any module criterion (no temperature can be choosen) again it is like there were no demon.
Finally assuming that there were an exact size door being useful for the demon work, then time would be the problem, when the door is open too long, both side particles can cross or collide, like there were no demon!, and if the door is opened too little time, then it only could "select" fast particles from both sides,then it couldn't separate temperatures.
I've read very complex arguments against Maxwell's Demon, concerning information store but I think size and time constraint could be enough arguments to defeat Maxwell's Demon, Do you know any related work about size and time constraint ?