Siege Cascade Bug?

Hey!
I've been playing Tactician, using the "Cannons, Ready!" Passive to proc ballista siege totems, which has been loads of fun. I've been using armor piercing rounds while leveling, but I was excited to switch over to Siege Cascade, since it would mean more cool explosions. However, for some reason, using siege cascade doesn't actually proc the totem's skill, even though the gem has the necessary tags for it to do so.

Anyone got any thoughts where I missed something, or is this a legit bug?