Elemental sundering + auto ignite helm

I made a simple build to clear mobs, just elemental sundering, the spear skill that detonates shock, ignite and freeze from monsters into an explosion, along with the unique helm that ignites enemies in my presence automatically. A lot of people crashes around me.

Since people can use elemental sundering without crashing others, I'm guessing it's some interaction between the skill and the unique helm. Maybe it's something to do with how the explosion doesn't happen if I run away from the monster and the ignite fades off, since they end up outside my presence aura radius, before the explosion has the time to fully blow.