hi. need help on the ground zero mission... i diverted the alien mothership (at least i think i did), however when i destroy the 2 towers to divert it, the green objective triangle disappears, it doesn't get check marked. but i hear the voice say :"it worked! it got diverted!". anyways when i finish the map later, the green objective triangle reappears with a red x. i'm pretty sure i destroy the 2 towers beofre the ship gets near it. is this a bug?