Thanks for the info ms21043, that appears to be a fairly normal Turbo-propeller controlling process. The normal operation naturally relies in being in flight mode, and in such mode the protections are conventional.
For this event, either two independent systems (LH PCU, RH PCU) suffered relatively uncommon failures in a very short period of time that inhibited the normal protections of the propellers, or some other cause occurred. The only common items to the propellers is effectively the:
operating envelope
environmental conditions
crew PL inputs (potentially)
The report will be interesting reading. For other operators of the Dash, you do need to be careful about movement of the PL's towards Beta inflight. Accidentally entering beta at high IAS and/or TAS could mean that you are relying on the perfect functioning of a backup system, or at worse there is no backup, and you are in an extreme condition immediately.
Any Turbo Propeller system needs care to ensure that Beta is not achieved in flight unless the aircraft has a certified mechanism to do so. Even so, they can have operational limits on such use.