Epic lair of lostmauth but?

I ended twice the dungeon, but I can't leave the instance till I use my special key to open the special chest (in talking about the key u buy with zen, or that you craft). In skirmish tuern u can open the chest, and close it if u don't want take anything inside without use key, but in lair of lostamut, look like we are forced to use key (and spend money)