Custom goal behavior

I've created a custom goal in Kangaroo 2 which applies a force in a direction defined relative to the current orientation of a rigid point set. The idea is that it should function like a rocket engine.

In order to test it, I've anchored the points in the set with a weak anchor. The system behaves as expected in some cases. For example if I use a force parallel to the line between points A and B, it converges to an identical solution whether the force is applied at point A or point B.

Additionally, if I break up a force acting on point A into two components (in the direction of point B and C, respectively), and apply both components individually to point A, the system converges to the same solution. 

However, if I combine these two ideas, and have the same components from the previous example act on points B and C respectively instead of point A, the system converges to a very different solution! I can't figure this one out. It seems intuitively obvious that if two effects on a system have a net effect of X, identical effects created in other ways will also have a net effect of X. But perhaps I'm missing something. Any insights would be appreciated.

-Evan

Edit: after testing this in three dimensions, it looks like was wrong about the solver converging to an identical solution when the force is moved along its line of action. Still not sure why it isn't, though