We've encountered some problems with the Vault of Stars.
1) In my oppinion, the gardener's green, red and black lines are sometimes not very reliable. Even if you stand inside the green and black line, the game occasionally ignores you and the flower or the guy under Nagoth gets hit despite intercepting the line. Rarely, I can't even see the black line as it pops up too late.
2) My personal favorite: The second and the third boss have a nasty habit of rotating their AoE attacks if you successfully avoided the red area. Sometimes it happens often, sometimes it happens rarely. This is unfair and needs to be fixed!
3) If someone with maximal skulls dies during the hedge maze and spawns outside (at the "fireplace" after the Prince of Frost), then the other players can't enter the final boss fight. Everyone has to kill himself, spawn outside the maze and do it again. When doing the maze again, all enemys except the last three behemoths reappear. It's a big waste of time.