had this problem on titan,i was healing my group(im using american servers since im originally from there,but im in belize studying abroad.) every time he turns around and starts his cast,im already doing a 180 around the entire ring and standing near to the tank when the cast is 50%(for those of you who dont know,i stand directly behind the boss,so when im infront of the tank, im stupidly far from the bosses cleave range) and i still get hit and sent flying.
tank said i was moving slow but then he noticed me near him after each swing and put it together that it might be some kind of split second lagg,as there was no way i could of been near him if i was moving slowly.