Looks like that quest only has 3 properties currently: unstarted, started, and finished. It appears to be set to started to mark wandering monsters as a possibility. When the quest is finished, that means you just beat your nemesis. But KoLAdventure, QuestDatabase, HaciendaManager, and ResultProcessor appear to be the only files that contain G04.
I suppose that means that this isn't a bug, merely a failure of expectations. And depending on what told you that it should be set to step3 at that point, possibly an incorrect wiki.