I don't know what changed, but sometime around when 1.3 released, it would seem that Prison Labor become incompatible with Prepare Carefully (In 1.2). I don't think these is any obvious reason for it, as it would seem to me that Prison Labor and Prepare Carefully don't affect the same parts of the game, but if I keep Prison Labor in my mod list, it breaks Prepare Carefully. I have also posted this in Prepare Carefully.