I am concerned about the (possibly correct) assumption that driver error is to blame, I recently had a situation on a 44 tonne shunting tractor used internally for hauling road trailers.
The ignition cut-out and when I applied the handbrake, it appeared to operate but had failed to apply the brakes!
A handbrake fault was found 3 days later only because I lived to tell the tale!

The vehicle is now "repaired" such that the drive axle brakes are automatically applied as the electrics fail and the truck can roll away again when the ignition power returns!!!
The full facts are outlined on another query on this page, I would dearly value some expert opinion - but so far I have had no replies.