We have checked all cables directly after incident, no damaged/broken ones found and all tensions seemed to be 100%. Aircraft was ground runned after incident (without any settings made to aircraft or prop) and technical crew reported that everything was OK. Prop went into reverse only when commanded too.
The strange thing here is that the flying crew thought initially (when taxing) that the Pitch Lock Regular has hung up and therefore pushed the throttle levers from Ground Idle to Flight Idle. As they did that the engine oil temperature and the prop revs went up. Torque stuck at 4,500 inch pounds. They looked outside and saw that the prop (#2) was in reverse.
Flying crew refused to accept the aircraft even after the ground runs and rigging checks have been done and everything confirmed as serviceable. A propeller was exchanged and the aircraft took-off. To date that same aircraft has been checked, twice for cable tensions and rigging, and has been run on ground profusely to establish if the "snag" don't recur. No signs yet. (Aircraft has done about 6 hours of ground runs before the snag occurred the first time during the pre-take-off taxi.)