Unfortunately I don't have a reference, the story comes only from oral tradition. I just performed a cursory search of the NTSB database and was unable to come up with anything similar.
As for low pitch stops, the PT6A-65/67 were equipped with an electronic low pitch stop that modulated between flight idle at 13 degrees-ish and ground idle at 5 degrees. Selection of the beta range in-flight was very possible. (Several accidents in the landing phase and my own "experience" point to this). As I believe you suggest, the cases I've seen of this have all been in an underspeed condition, i.e., off the governor. I can't say for certain what would happen at higher speeds.