I would say the biggest diference in a Spit-1 when inverted would be the engine dieing out and eliminating all propwash.
Then again maybe its the aerofoil shape issue? The usual nose down pitch moment is to a degree a byproduct of the lift being developed over the wing. Hence aircraft arent designed around the CG, but around something called the aerodynamic center (about which this moment remains contant at all angles of attack).
If its not a symmetrical aerofoil, then when inverted the pitch moment generated by the aerofoil would differ. Im just not sure if AH actually emulates aerodynamics at such a level tbh tho.