The adjustment screw for the turntable bushing is used to add "drag" on the turntable. There is no reason for it to be spinning around like a top.
There is nothing wrong with it and you do want it to stop when you stop pushing/pulling the turntable into position. So, don't worry about it.
Also, many new users think it is a brake and will lock the turntable into place. It is not a brake and will not hold the turntable in position, no matter how tight you tighten the set screw.