That might be the case, yes. I don't know Joiplay too much, but the website advertises a 70% to 90% compatibility rate. It is possible that Joiplay does not like the way saving works in TPH. I am afraid I do not have a solution for that at the moment.
Does saving and loading save files work? If only the persistent variables used for the gallery do not work, you can still see everything the game has to offer, you just won't be able to see the gallery.
