I can't remember if this is supposed to happen: I holy warred for the 2 highlighted regions below (the duchy of Saxony which was owned by an independent slavic ruler). The actual duchy title belonged to someone in the HRE who owned all of the de jure area of the duchy of Brunswick (but the Brunswick duchy title didn't exist). So, now that I own 2/3 of the duchy of Saxony, I usurp it and steal every single vassal count the former Duke of Saxony had (9 counts in total as you can see by the shields).
Is this meant to happen? Or is this one of the dangers of owning none of the de jure counties that are associated with your title while having no 2nd title of equal rank to it?