No Man's Land + Siege Engineering?

In the Explosive Traps tree, there are two nodes called “No Man’s Land” and “Siege Engineering.” No Man’s Land causes you to fling out a dozen traps in one go, which is a real blast (pun intended). Siege Engineering summons a ballista when one of your traps explode. I thought it would be fun to tinker around with explosive ballistas on top of the explosive traps, but it seems they’re not proccing with No Man’s Land laid traps.

Is this intentional? If it is maybe I’m missing something in the descriptions somewhere? And if it’s not, well perhaps I found a bug in the interaction between the two nodes.

Update: I despecced then re-specced into the skill and it seems to be working now! Either that or I just got really unlucky with rng in my initial tests. Either way yay exploding ballistae