458 Aftermarket Sports Exhaust - Triggering Check Engine Light

A quick question for everyone, thanks in advance...

I have a Capristo exhaust on my 2013 458 Spider. I've had it on the car for over a year with no problems but recently a check engine light came on and off to the dealer the car went. I got a call from the dealer last week and they said that the exhaust was changing some of the parameters and was triggering the lambda sensors in the cats (cats and sensors and everything save the back boxes remain OEM).

Is this a problem that others have had when fitting an aftermarket "cat-back" exhaust? I've seached the forum several times and cannot find anything. If so is there a "fix"?

Incidentally, Maranello are also trying to void my warranty. Luckily it doesn't work that way in the UK (Capristo is the only modification on the car and doesn't harm anything), but the fact that they are trying regardless of the law of the land is a bit off-putting. They are saying that if I buy one of their OEM sports exhausts for a cool £4700 that all will be forgiven...