I don't know why it happened, if it was just luck, or what. Anyway, what happened was I was dueling a hunter in the guild whilst waiting for the rest of the raid to do the eye. He initiated the duel first, and I clicked the duel button and his pet was attacking me, but it was still friendly! I couldn't even find the owner at all! Even after the duel (and I lost of course) he said he was jumping on me and crap but I couldn't see him anywhere, just his pet. He dueled another person and the same thing happened:Only saw pet and was still friendly so couldn't be attacked. We checked to see if AoE's would work, and they did do damage. Then we noticed something: His ghost was right at the graveyard. I used /target (playername) and it just went to his ghost. So he dueled a lock and he said that the guy was sort of blinking all around, hard to target. When he did attack him, some of the raid said, and I saw it too, he was attacking the ghost (Like with the green drain life thing went straight to it). So I asked him what happened on how he died, and he said that he dueled someone, and a horde ganked him with one-shot at the end when he had 1 health left (there was a guy doing this to people earlier, probably the same one), then he clicked where the resurrect button was, but he did it before he got ganked and clicked it before it showed.
I don't know any horde to recreate this glitch, so someone else will have to try it out, see if it wasn't just all luck or whatever happened.