Ok ok ok. I just took over the Kingdom of Denmark. Previously I held the two Duchies of Ostergotland and Smaland. The elective laws there were Agnatic-Cognatic Gavelkind. The election laws in Denmark are Agnatic Elective. However, when I first took Denmark the nobles were set to elect the son of the last king that had just died as king, upon my death. For whatever reason they then choose to elect my eldest brother in his place. Along with that comes the two duchies, for whatever reason and they do not retain my eldest son as their inheritor. If this makes sense, could someone explain it to me?
Elective passes all titles if the election goes to someone in the same dynasty. Otherwise you'd end up losing most of your titles whenever you elected someone other than your eldest son.