In terraforming Mars, I'm trying to dampen the precession of obliquity (which is not simulated by USB), by using Ceres as a stabiliser in a similar way as the Moon does for Earth. However, whenever I select the parameters of Ceres' motion, it keeps getting ejected from orbit around Mars. Why does this happen, even though the orbit velocity is determined by the auto-orbit function? Or more generally, why does this sometimes happen for instances where the main body is in motion?