But regardng the fire extingusiher, both of my feet were on the pedals for the entire flight, for the entire landing, taxiing and for braking, so I dont' think it was that, it was a solo flight. I'm not convinced it was the fire extinguisher tbh.
I did have someone at the landaway airfield look at it and he found nothing, and I spoke to the club (and I have the guy who looked at it speak to my club) and I spoke to someone else at my club and if they said it was safe I would believe them (more on the grounds of my own inexperience rather than any self-preservation), But I take on board what I thik you are saying, ie: I should have not flown it back that day unless it was formally investigated.
Regarding shut down, as far as I can reacall I shut the aircraft down in the normal way. But can't link the smoking stopping to a specific action.