Kiddushin 15: Cross-generational Talmudic Debate

More on the gezerah shavah between "sachir" and "sachir," with regard to how this indentured fellow goes free - aside from the jubilee year, which is already specified in the verse. But Rabbi Yehudah HaNasi doesn't use this gezarah shavah, so why not? And why the disagreement over this? Plus, how does a gezarah shavah really work? How does one be freed from one owner only to be enslaved to the relatives who freed him?