Dynamic game theory in action

This story, from here, is probably not true.

Three economists and three mathematicians were going for a trip by train.Before journey the mathematicians bought 3 tickets(they could count to three)and the economists only one. The mathematicians were glad their stupid colleagues were going to pay a fine. However, when the conductor was approaching their ompartment, all three economists went to the nearest toilet. The conductor, noticing that somebody was in the loo, knocked on the door and in reply saw a hand with the ticket. He checked it and the economists saved 2/3 of the ticket price.Next day the mathematicians decided to use the same strategy - they bought only one ticket, but the economists did not buy tickets at all. When the mathematicians saw the conductor they went to the loo, and when they heard knocking they handed in the ticket. They did not get it back. Why? The economists took it and went to the other toilet.