Blade Sailing
Vfr,
This is correct and quite normal, it's known as blade sailing. Rotor blades rely on centrifugal force in order to maintain sufficient rigidity in the flap-wise direction. As the rotor speed decays, the centrifugal force reduces more rapidly than the aerodynamic force and therefore very large flapping motions can result. The effects are most pronounced for ship-borne helicopter operations where high winds and the turbulence around the ships superstructure result in rather extreme conditions.
Hope this helps
CRAN