Kungen в своем блоги пишет о том, что когда они убивали Иллидана, то близы смотрели за килом и фиксили баги прямо между траями.
Я уверен, что сейчас Близы так же следили за траями Энсидии и решили ничего не делать.
Так же он приводит список боссов, которые были багованы. Vanilla
Onyxia: It was possible to stand on ledges to avoid getting feared into fires.
Ragnaros: Impossible and got nerfed several times before he was killed.
Nefarian: I didn't know any bugs on Nefarian myself but I was told that you could have more than 40 people logged out in the room and if someone died you could just have another guy log in and take his place. You could also soft reset him to get more tries when you had used up your (1 hour?).
C'thun: Bugs all over the place and impossible.
Kel'Thuzad: Chance to despawn for the whole reset if you left the instance. This happened to us after we had wiped at 1% twice during World first attempts. Yes we weren't exactly happy at that point.
I actually had to struggle to find bugs in Vanilla. I guess it kinda proves that Vanilla was the best and had the most capable people working on it :).
The Burning Crusade
Gruul: You could use Limited Invulnerability Potion to avoid his main ability Shatter.
Magtheridon: Bugs all over the place and fixed a week after our kill (to an easier version)
Lady Vashj: Same deal as Magtheridon, the fight was bugged in more ways than you could possibly imagine and it actually took months for them to fix it.
Kael'Thas: Impossible, adds had no threat among other things. I don't think a single part of the fight was working the first time we reached it. Fixed a week or two later.
Archimonde: Several bugs the first week, it kept resetting among other things. Sk-Gaming even focused on Hyjal since we already were far in Black Temple just to find out that Archimonde was bugged and impossible to kill. Fixed a week or two later.
Illidan: The first version that only Nihilum and SK-Gaming attemped had a few bugs and funny enough Blizzard actually fixed them between tries. Good job there Blizzard!
Kil'Jaden: You could avoid getting add spawns with Bubble and Iceblocks.
A great expansion with bugs on every single end boss and most of the normal bosses as well.
Wrath of the Lich King
Malygos: The first few days he had a couple of bugs such as doing double breaths and a few other bugs I can't remember.
Algalon: The first weeks when only Ensidia had access to him he wouldn't get out of combat so we weren't able to reach his room for another try.
Anub'Arak: Holy Wrath bug which was used on the World first on purpose. WRU bans?
Arthas: A bug in phase 3 that made the room bigger. Which apparently was caused by saronite bombs. Something I'm not exactly sure about since they did 0 Siege damage during all the tries. Wouldn't surprise me if it was something else that caused it.
Same deal as The Burning Crusade. Bugs and more bugs!
What I'm trying to say is that EVERY SINGLE end boss since Vanilla has been bugged.