I have not seen duplicate slaves happen in recent versions, nor has it been reported by anyone else so I would expect that it is specific to something you have done or to your save file. The most likely cause would be installing additional mods besides the 2 required, Improved Random Portraits, and Constants; so if there are any additional mods, then please list them or remove them.
I would recommend not saving any progress with duplicated slaves as there can be multiple causes that can behave in weird ways, such as having two buttons for only a single slave. You may also want to consider getting the Debug mod to check for errors.