If you select an ACU and an engineer you are somehow allowed to OC
that horrible video explains that a bit http://www.youtube.com/watch?v=dSOz6xk-Vhw
also when you OC with '4000' power in bank you will get '-1000' in bank, so it screws your eco a bit
ZeP said that he has no idea how to fix it, so it is up to you guys... Please try to fix it...