I had a similar experience: 25mph, clear road ahead, horrendous scraping noise as brakes locked on. Fortunately they released after about half a second. The only notable thing was that the temperature was below freezing. This was before I had the software update, but there's no suggestion that the software update would have made a difference.
I'm trying to get into the habit of touching the brakes every time the "Brake!" warning flashes up, because pressing the brake or swerving overrides the automatic braking.
I agree with you that it's a very frightening experience.