First answer this question: If there is no predetermined jailor but there are random towns and someone prefers jailor, does he get the role jailor? If no, ignore the question below.
If you do -prefer role (with 20k points of course), it's supposed to give you that role, right? And mason never gets ransomed without a second mason, right? So what happens if someone prefers mason in a game with no predetermined masons and at least two random towns? Is another person forced to have mason? Does he alone get mason? Or does he not get mason at all, going against the role prefer description?