Of course if I intentionally wiggle the plastic knobs, they will move a little sideways. Surely these are not as rigid as the knobs on my Minimoog D, but these aren't industrial grade, big heavy duty, sealed Allen-Bradley army rated potentiometers costing $30 each either !
I agree with gilesjuk, pots are supposed to be turned not moved sideways. And, on my OB6 desktop at least, when turning them they feel rock solid.