we seemed to manage for very many years in RAF and RN doing it - the only problems encountered were usually when the rad hold was left engaged as you coasted in - that resulted in a large upward movement of the collective on the Mk3 and lots of shouting
The radalt might lock onto the seabed in very shallow waters in very calm conditions (on old installations) but that probably accounts for a minute percentage of the user spectrum.
Never, ever heard of this phenomena before despite hundreds of hours overwater in flat calm (non doppler) conditions with radalt hold.