So just wanted to share a hint with those who like me happens to catch a bug with web not beeing broken on the last boss.
Firts of all it is realy nice bug, because you dont have to fight tons of adds.
Secondly dont be too upset about not beeing able to turn in quest the answer is here.
Teleport back to the start of the dungeon, go forward to the first or second boss room (i don't remember exactly) and there you will suddenly find a quest giver torturing the last boss.
There you will be able to turn in quest normaly and finaly recieve your rewards.