Trash mobs killing my group WTF?

I know the deconstructor's adds were bugged. But my 10 man couldnt seem to down the molten constructs that were in front of Ignis. The mobs were silenceing the healers when they came within 30 yards of em to heal the tanks...so we would die. Even poping all CDs on them we managed to down 1 of them...are we missin somthing?

Edit: I should note that we did this instance blind (we didnt look up any strats or problems before we whent in).