A few people above have told you why the boss resets. Why are you not listening to them?
Desperatu and Gothrock - read their posts....
More precisely, it's about immune pets, like shades or netch, so dismiss all un-damageable pets before the fight. Yes fashion pets too.
The mobs try to target the netch, and since it's labeled immune , they just reset the whole fight.
A soon as we got rid of all stupid non kill-able pets, it worked just fine.