Maule M7 by Pilot Experience Sim

I just got the plane and really like it so far. Great for little dirt strips in Idaho and such.
But is it just me or is it not possible to add any payload? No matter what I enter into the weight fuel panel it always resets to the default empty loadout. I know I can set the co-pilot via the tablet, but how can I get a full plane with three passengers? Any insight would be greatly appreciated.