Quel'delar fight: The Halls of Reflection

I have a problem in the "The halls of reflection" quest (https://www.wowhead.com/wotlk/quest=...-of-reflection) , i go to the dungeon, in normal 5 man, i start the fight but the sword seems permanently enraged, it never stops spinning and doing massive damage, i brought a tank friend and it melts us both, it does so much damage that uther can't attack it, it stunlocks him. I watched videos of the quest and it looks nothing like mine, in the videos quel'delar attacks like a normal mob not in permanent bladestorm.

Anyone can help me? This is what i tried:

Restart the instance, drop the quest and restart the instance, stun the creature, bring a friend, see if im not in a raid (im not).

Thanks for the help