I just started a game with Lithuania and released Zaporozhie as vassal and chose to play as Zaporozhie. Ofcourse I started a war for independence, except that I only wanted to take land and not get independence. It was easy btw, got Novgorod, Muscovy, Hungary and Denmark with both PUs to help me against Poland and Lithuania (Poland was at war with TO). But that is not the point heh. The point is: When I took land from Lithuania and stayed the vassal, they started giving me all cores from the land I took from them, so I didn't have to core ANYTHING. Is this intended? They probably wanted to reduce my liberty desire (which was at 100 and now is at 30).