No, this should not happen. It's the result of the factory that made the scope cutting corners with costs, using bolts that just don't perform the way the bolts should. Not Bintel's fault at all.
There are a couple of solutions. If enough of the bolt clears the nut when it's tightened, you could use a second nut to act at a locking nut. Just don't over tighten the nut closest to the base as this can lead to other problems if you over tighten the ground board to the rocker box base. The second solution is to replace the existing nut with a Nyloc nut. These don't come loose either.
There is a little ball-bearing washer that isolates the knob from the rotating base. Maybe it doesn't rotate freely due to contamination etc, or maybe the bolt assembly is not put together correctly?
