VEHICLE WAS PARKED. PRESSED BUTTON TO HAVE REAR POWER LIFT GATE OPEN. AS IT WAS FULLY OPENING, I PUT ONE OF MY GROCERY BAGS IN THE REAR HATCH THE LIFT GATE POWERED DOWN ONTO MY HEAD WITHOUT WARNING. IT KNOCKED ME TO THE PARKING LOT. WITHOUT ANY DIRECTION FROM ME IT WENT PARTIALLY UP AND DOWN AGAIN AND THEN CLOSED FULLY. I GOT UP AND TRIED THE BUTTON AGAIN TO OPEN THE LIFT GATE. IT OPENED AND THEN JERKED DOWN AND THEN UP AND THEN CLOSED. IT STILL MALFUNCTIONS THIS WAY AND WON'T OPEN AND STAY OPENED.