As understood by Gibbs, and reemphasized more recently, this is a misuse of Gibbs' non-extensive entropy quantity. If the gas particles are distinguishable, closing the doors will not return the system to its original state – many of the particles will have switched containers. There is a freedom in defining what is "ordered", and it would be a mistake to conclude that the entropy has not increased. In particular, Gibbs' non-extensive entropy quantity for an ideal gas is not intended for situations where the number of particles changes.