I have for some reason died from Benevolent Bismuth on my Guardian around 5-10 secs AFTER I've already killed him. This is not the first time I've died to him for some mysterious reason. My guardian has over twice the hp and over twice the defense of my wizard and priest, and yet I appear to take much more damage from him than my priest and wizard (I should be taking less than 1/4 the damage in terms of % of health).
I had killed the boss and then finished off the trash mobs but noticed my health dropping fast. A few secs later I was dead. So this time I checked my combat log and noticed I was killed by "Benevolent Bismuth killed you with mofodiebis10_name". During this time the only damage I see in the combat log was series of 59 hp damage I think from the dot in the dungeon. This comes out to only around 0.1% of my health per dot, yet I was watching my health drop by around 5-10% per sec. I think I went from around 20-30% health to zero in about 5 secs after everything is dead.