X380 Stops very sharply, hurts neck

I have an brand new JD X380. Love the mower. Love the new deck design by JD. However, when backing up and I take my foot off the reverse pedal, it stops NOW. It whips my neck, or back, and if on pavement, sometime the front tires come of the ground. JD dealer says: they are all like that (i.e. we do not know how to fix it) or they say: "it is a safety feature designed in by JD so you do not back into anything (i.e. blame it on JD). My wife will not mow with it any more. I am some what learning to brace myself. I would exptect is to slow down gradually like my X300 did and like the X380 does if you are going forward. Any thoughts???

It has a shock absorber check to see if that is not binding.

Thanks. I will check.