UEF, the mission where you first get the Buzzkill missile defense. I built it and it shoots and kills my ACU. I have the Missile upgrade for the ACU, so maybe it's shooting at the missile in the ACU? I've searched, but found no references, so I was wondering if anyone has had the same issue.
It was funny though, when I heard my commander was under attack and I was just in time to see my own building killing it.