I assumed, wrongly, that move towards with a force action uses top left object coordinates as reference. Instead it uses object/sprite geometrical center. So if I set an horizontal or an vertical motion I got a diagonal one instead. I routed this adding object center coordinates to destination coordinates.
Then comes the question:
Is this a bug or a feature of this action?
Well, I would say that in most cases, you don’t want to align to one edge of the object, using its center makes more sense… As long as this behavior is consistent with other move actions, I wouldn’t call it a bug.