So now I have to retract vasselage of the Duke of Normandy from the King of France. On the Direct Vassal Map Mode France now has this single county in Germany.
Some count who is under the Duke of Normandy who is under the King of France who is under me (HRE) inherits another county somwhere in Germany. I am enforcing this with tyranny weighted against goodwill I build up with long reign and massive diplo leaders. Dukes must be restricted to their de jure duchies. Internal border gore is not acceptable for me.
So it seems despite being lazy and unorganized in RL I suffer a heavy case of OCD in CK2.