PS: the problem can occur more often when a) you park the car in the sun, leading to higher pressure in the tank, and thus overflow of gases into the combustion/emission track (emission mixture too "rich"), and/or b) "topping" the fuel tank and manually adding more fuel than the automatic of the petrol pump nozzle does, thus leading to a "too full" tank (see a.)
I also noticed that with higher age of my Roadster, this happens more often (even after replacing the lambda sonds).
