I noticed that when playing with just a keyboard, when throttling down using F2, I sometimes accidentally went into reverse thrust. Perhaps check if your throttle bind for thrust axis is set to (-100, 100) instead of (0,100), or a reverse-thrust toggle is somewhere double-bound.
Not sure if this is possible with the aircraft you mentioned, but the Cessna Caravan at least has no objection of you reversing thrust during flight.