This is the 4th time since purchasing the truck that this event has happened with time having the most severe results. When shifting from reverse to park the shifter goes into park and jumps back into reverse. First event (after exiting the truck) the truck rolled into a shipping dock breaking a taillight and buckling the rear bumper. Next two I had one foot on running board and one foot in the truck ant was able to hit the brake stopping the truck. This fourth event one foot was on the running board and one on the ground. As truck went back the door flattened me to the ground and the front tires rolled over both of my legs. The truck rolled up an inclined parking lot, across a busy road and down a bank. I was driven by ambulance to the hospital and then transferred and airlifted to trauma center at Ruby Memorial Hospital. After the second event the local Ford dealer said they could not duplicate the event. The brakes do not hold even though they are depressed and set when the shifter is shifted.