Those with any knowledge of twin turbine engined helicopters will realise that this is completely normal. The collective lever controls main rotor blade pitch and the engines respond together to maintain rotor RPM. Admittedly, there is only one main rotor on most helicopters but obviously the Chinook and Tilt Rotor have two.
Individual control of the engines is done by separate controls. These are not normally moved because there is no need in normal use.