....Jerry, I'm guilty as charged. I never set the park brake but I do leave a vehicle in park or in gear most of the time.... does the fact that the jack will "roll" as you lift not count on a smooth concrete floor?? Just a thought.
I agree with jack stands and depending on the reason I can see chocks being used. My day had MANY mulitiple broken ribs when a vehicle "rolled off" and on top of him. 1960.