I have never had an issue with any of these cameras giving me the wrong exposure. The only reason I used the incident meter was because I was shooting slide film. Of course I expected there to be some difference in the meters but not 2.5 stops! The scene was a product shot light with two photo spots through white umbrellas so the scene was lit consistently.
Did you take a picture on the slide film at the incidental light reading ?, and if you did what was it expose like ?.