Well this happened to my twice last night on Kephess, I was between 30-40m behind the boss, there where ranged and healers in my way yet they lived and I died from savage arcing slash. Kephess was facing away from me.
The first time I had dropped 4 circles about to drop the fifth and got one shot for nearly 23k from savage arcing slash. I was clear of the previous purple circle and the smuggler in the way got no damage but yet I was killed. The second time we had a sage healer and a smuggler in between me and the boss, I dropped one circle when to drop the second and then was dead, yet again clear of the purple circle and dead. Yet again nearly 23k with the message savage arcing slash.
So this must be a bug, has anybody else experienced this? It cost us our first Kephess kill as a operations group so not very impressed right now