Test Your Metal - Ash Legion Turrets don't work

[Anders.4275]

Was doing the Iron Legion lvl 10 personal story quests. During the "Test Your Metal" instance, I was doing the part where you test the Ash Legion turrets when I encountered this bug. I set up all three turrets and had the ghosts released, and the NPC told me the ghosts would ignore the turrets and go for his troops. However, the ghosts swarmed and quickly destroyed the turrets instead. I could not get more turrets from the box- once they were gone, they were gone, and I had to fight the ghosts without any turrets because they were all destroyed in the first two waves. I still cleared the instance fine but it was annoying that they weren't working as expected.