I have a Mad Catz Fightpad, which shows up in Retroarch as a standard Xinput controller.
The only problem is that the right bumper is assigned to LT - this is by design on the Fightpad - and the actual RB button is one of the six face buttons.
I’ve tried to assign the right bumper to RB in RetroArch, while assigning the button labelled ‘RB’ on the gamepad to quick Save State. That works, except when I press the button to save state, it also sends RB to the game - as if both my remapped button (the right bumper, labelled LT on the gamepad) and the button labelled RB are now hooked up to RB in the game.
I have no idea how to fix this. Game like Super Metroid really do need the shoulder buttons to be mapped correctly.