This is actually a bug present on live too, however I just looked into it more: When standing in lava and taking damage - the damage dealt is counted as sourced from the player.
Experimenting with
@Stormahawk in Stonefalls today, we discovered that proc sets like Illambris and Burning Spellweave will trigger, among other things. It seems pretty much anything that procs off damage will trigger.
If you die from the damage dealt by lava it triggers "kill" based procs. I'm a werewolf wearing Vicious Ophidian, so when I died I triggered the 9 ultimate gain from Banish the Wicked in the FG skill line and VO Stamina return.
The damage from lava also scales off champion point passives, I saw a direct increase in the damage I took from placing points into Elemental Expert.
Perhaps this is due to the fact that lava is actually coded as a buff rather than debuff?
While I'm at it I'll mention something I wanted to bring up a while ago and that is the lack of consistency with lava damage. It varies based on zone due to the multitude of abilityId's for it. Is it really necessary to have so many abilityId's for lava - could just use a single id and fix it to be a debuff for all lava in the game.
EDIT: Also I'm not sure every single type of lava causes this. It would take a bit too long to run around to all the zones and test every id.
Edited by ArtOfShred on April 21, 2017 1:37AM