Westcliff, I have a vortex viper 6.5-20x44, and it has the same kind of turret, you lift against spring tension and turn, then slide down on the correct spline to set your zero. I see what your saying, how it could happen. I have had this scope for 3 years on my rifle. It has NEVER happened while in the field hunting, shooting praire dogs, a few deer at 300 or more yards, or just shooting steel. I see your point, and I was concerned at first as well. BUT. If your aware of this, there is a simple fix. Don't lift the turret when you turn it. I put slight downward pressure when I turn. It's not hard, it doesn't take any more time.
Now, if I handed my rifle to someone that didn't know, and they dialed for a long range shot but didn't know how the turret worked, it's POSSIBLE (but not likely) that this could happen. Though, with the multiple people that have shot my rifle and dialed in the correction I gave them, it never has.
I have no experience specifically with the nikon turret, but if it's anything like the vortex, it is really not an issue if you know about it. Just my thoughts.