In short, I planted the bomb and was guarding it. Two Aura’s ran in to defuse it, so I ran in there, threw a nuclear pancake at them, pushed mouse1 to shoot it, and for some weird reason my character decided to try and start planting another bomb when I pushed mouse1 instead - Even though my other bomb was still there and active.
Not entirely sure why this happened, because my plant key is not mouse1.