Armour Explosion doesn't trigger with Mirage Archer attacks

I'm using Mirage Archer with Armor Piercing Rounds and Armor Explosion. The Armour Explosion support gem doesn't seem to trigger when the attack is made by a mirage archer, even after all of an enemy's armor is broken. When firing the skill manually, Armour Explosion triggers as expected. I've confirmed that the armor break is being triggered by the Mirage Archer and not any secondary effect.