Inertia dampeners do not account for attached grid mass in gravity
How to reproduce:
* Be on a planet with gravity
* Build a heavy brick of anything, heavy armour will do.
* Build a ship with ample upward thrust and a landing gear on the bottom. Make sure there's plenty of thrust to lift both the brick and the ship.
* Lock ship to brick
* Lift off
* Stop all user input
* Observe ship start slowly sinking towards planet, despite having ample thrust to stay afloat.