I'm confused on how exactly is gavelkind succession supposed to work. All I've read (e.g. Crusader Kings 2 Succession Laws – Explained says that the highest titles I have will be split between my heirs. But that's not what I'm seeing.
Currently, I'm the king of Bohemia, Germany, Bavaria, Italy, Sicily, Norway and Lithuania and all of them are Agnatic-Cognatic Gavelkind. I'm also vassal of the Holy Roman Emperor and I have two sons (both are young and neither of them is a bishop). If I make Germany my primary title, the game warns me that I will lose one Duchy and one County (both de facto belong to the Kingdom of Germany) to my second son on succession. If I change my primary title to Italy, the warning goes away.
Because of this, it seems to me the explanations I've read are wrong: According to them, I (as the first son) should keep the primary title (say, King of Germany) and my second son should get at least some of my other kingdoms.
Did I misunderstand the articles I've read? Are they wrong? Or is my game bugged?