If you put the planet on an elliptical path arround the Sun in the System Manager , the system does not save it. You can change it but it is not accepted. If you orbit a Moon around a planet and the planet will be removed , they still move around the sun like with a planet . Normally, they should be automatically set on a path around the sun. If you press the build button , the system should be saved as a file so that the game must load this file only . Currently, it is so that you press the build and save button but the game still generates an new planet .