I suggest you have a good look at the little pinch bolt in the end of the carb heat quadrant. Mine stripped allowing the operating wire to slip through, giving all manner of strange behaviour and defying several engineer inspections (until it broke over the Irish sea!). I think it would be possible for the carb to stick in 'hot' after landing and not be noticed until the next day when exercising the control and it flops over to 'cold'.