i believe its a single stage. i detailed a fellow p5 owners car. his is a vivid yellow. its a single stage, because the wax i used (nxt 1.0) is a synthetic wax that has mild cleaners in it. yellow was coming off on the applicator pad, as well as on my microfibers. this means that the clear coat is mixed in.
get some cleaner wax, like mothers, apply it to the area where the clear has peeled away, and then apply it to the area on the spolier that isnt peeling. when you wipe away the wax on the area that hasnt peeled, and there is no yellow on your microfiber, that means there is a clearcoat on the spoiler and its peeling off.
it could be that the body panels, and the aero panels were painted seperatly than installed...