Pious Upbringing doesn't reduce the mental stamina required to pray. You still spend 25 mental stamina with or without it, at least according to the game. I think it may have to do with the fact that I already had a God and God Loyalty to begin with, but still chose the same God anyway.
Also based on how the trait is explained, this part may not be a bug but worth mentioning: if you already have a God before taking Pious Upbringing, but do take it and then choose that same God, and your Loyalty is below 40, it does not shoot up to 40. You also still expend the same amount of stamina (25).
Also based on how the trait is explained, this part may not be a bug but worth mentioning: if you already have a God before taking Pious Upbringing, but do take it and then choose that same God, and your Loyalty is below 40, it does not shoot up to 40. You also still expend the same amount of stamina (25).