Low mass components exert greater gravity force

[codereptile]

I have crated a simple ‘rocket’. It consists from a static mesh with a mass of 100kg and exerts a force of 100 * 9.81 Newtons. In this scenario, the missile hovers in place, as expected.
Then, I added a cube with a mass of 1 KG and tied it to the rest of the rocket via a physics constraint. Now, I’ve changed the booster force to be precisely 101 * 9.81 Newtons, but the missile drifts down quite significantly. I’ve played around with the force and found it to be ~120 * 9.81 Newtons to hover.

The reason I believe this is a bug, is that if I then change the mass of the cube to 20KG, it continues to hover, meaning that the gravity force is incorrectly calculated for objects under 20kg of mass.

[codereptile]

After some initial testing I’ve found that the issue is with the physics constraint: without it, the problem doesn’t appear (if I just place the cube onto the missile). Moreover, I’ve found that if the missile AND cube have roughly the same mass - then the scenario works, even with the physics constrain and low mass

[codereptile]

This is very weird, but swapping the component names solved the issue. So the cube should be component name 1 and the missile body - component name 2. This feels like a bug - why would swapping the components change anything?