With #1 and #2 engines off, our initial APU start is always with both ECS switches in the OFF position. Company SOP's are fairly straight forward in that regard.
I'm talking about the APU start after landing at an airport with the intention of shutting down. #1 and #2 engines are still in FLY as we taxi towards our ramp and go through the "After Landing Checklist". The last item on that list is the APU start. Sometimes it happens that we start the APU with the ECS switch in the HEAT position. SOP's and checklists are not 100% clear about this I guess. That's why this situation sometimes occurs and we then get the fuel odor in cabin and cockpit.