Walk Behind Lawn Mowers

Hazard regarding Husqvarna self-propelled HU550F. I recently purchased this mower from my local lawn machine business (not big-box store). My son was mowing the front lawn on the low setting. Mulch side door of the mower was closed. He was walking toward the front of our garage (on the grass, not in the driveway), approximately 30 feet away. Our new (to us), six-day old SUV was parked IN the garage with the front door open. I was standing behind the vehicle, facing the back of the vehicle, off to the left side, reading the owners manual. Within an instant, following what sounded like a gun shot, the glass hatch of the vehicle was shattered into a bazillion pieces. We suspect that a piece of item #4 stone that had been lying in the grass since plowing season many months ago may have been lifted by the blade and shot toward the car. Note: this lawn has been mowed at least eight times since spring over this same spot with my former, now broken, mower. Needless to say, this was quite shocking. Besides being soooo thankful that it was not my skull or body, my children, or the dog that this rock hit, added to the mess of the glass and the EXPENSE to replace the back window, we are now very leery of this machine. In comparing the fronts of my two mowers, the design of the front of the housing may have added to this freak accident. Even at its lowest setting, there is still a 2 1/8th" clearance(compared to my broken mower that has 1" at its lowest setting). The bottom rim of the front of the housing of the Husqvarna rises up across the front of the mower once it passes the front wheels. Thank you for your consideration of this potential for this machine to cause significant damage (or potential significant bodily harm). Perhaps your engineers and quality control experts will take the design into serious consideration when doing any upgrades. We had taken all reasonable precautions: the car was inside a building, no humans or pets were 'outside.' (Even with the garage door closed, I predict that a hole would have been left in the front door.) Please let me know if you need any additional information or have additional questions. I look forward to your comments.