Ive not see the actual rule, but my understanding is that mana burn is only supose to do 4x damage to mana, so 100 points of damage would also do 400 points of mana burn. This has never been the case, because mana burn has always burned it all away. Im running a hammerden with base mana this ladder season, so as Ive gotten to nightmare and hell, there is no way for me to tell. Any hit from a mana burner would burn all my mana. But a couple of times in normal I had a little mana left after I got hit from a burner. It could be from a couple of other things, I do have some mana per kill and % damage to mana. My best guess (Ive had some time to think about it) is that I had some kills after the burn from hammers still floating around. I was hoping that people with a larger mana pools would know for sure.