Thanks everyone for reply - much appreciated! I am completely new to mmo so was really confused at the time.

If someone was indeed dual-boxing, it's probably not ACN as he was the one who initially complained and he did speak out in support when I questioned the CNJ. Thinking about it... the tank never said a thing during the run, and while we were questioning CNJ, tank just kept running and pulling. Before the 2nd boss ACN and I were standing outside the boss room when I tried to vote kick, and tank literally ran in and pulled boss... so maybe he does know something...

Oh well anyway, I am glad that this is a very rare occasion and I really hope no one else would encounter situation like that. It's rather unpleasant.

Thanks all!!