In virtually every helo I have instructed in, the collective pitch should be lowered smoothly once ground contact is had on an autorotative landing, even while running on.
Excessively low rotor rpm while the craft is moving (exposed to lurching and varying winds) is a bad thing, and any movement of the cyclic while in that state could lead to blade-fuselage contact and a major problem.
This does not mean that you dump the collective, nor do you force strong ground contact, but you must not leave the lever up any longer than necessary.
I have no Robinson time, and certainly defer to those who do and advocate something else, but leaving the collective up is certainly not the norm for helicopter autos.