— Inertia Dampeners do not work well with gravity: when the engines are in non-default mode, the dampeners over-apply thrust needed to hover the ship, causing it to drift upwards at some constant speed (values from 0.6 to 2.5 m/s were registered). This is hard to work around and in fact requires fixing of old game bug with ThrustMultiplier being ignored for WASD and dampeners, so, until there's a decent workaround or the bug is fixed by KSWH, try to avoid prolonged use of engine modes > 1 on planets or moons. Remember, it's always more fuel-efficient to build more engines than to overclock them.