Hey there, Tidus here, GM of Ambient 4/4 H EC 16 clear 4/24/12.
Here is a link to a video of one of our Kephess attempts the other night where Kephess managed to one shot a tank with "Arcing Slash" when the tank was 20m behind him, and while Kephess was casting "Breath of the Masters".
You'll see the tank Tidus, me, on the left marked with Crosshair randomly die due to "Arcing Slash" from Kephess WHILE Kephess is casting "Breath of the Masters". Note he also manages to do this without changing targets and without moving.
We've killed this many times now, and have only seen this once this week after this most recent patch. I'm not looking for feedback or anything, just thought it was hilarious and there is definitely something wrong going on here.