You could expand the options for inversion in x and y direction.

I'd expect y-rotation as in flight simulators, maybe the x-direction is ok but it is hard to say if only one is not as expected.
You try to concentrate on doing it right but there is still the second dimension you have to take care of. (It is even more complicated if only one direction is inverted than two)

I'm sorry... that's the "tick" I used in Dragonrise for the confusion effect, invert x, y or x & y koordinates of the screen to irritate the player's brain for movement...