Ok I donít know if this is a bug so much as a flaw, but you can play all levels invisible yes I said invisibly here how.
Start the mission then beam or warp out for the next step you have to have your auto instances disable so you can pick your own instances. When you beam or warp out it will say you will lose what you have completed push ok. Then your choses of instances will pop up push cancel and boom your invisible. You can the shoot and kill the enemies and they donít shoot you back. You can pick thing up set bombs talk to people and everything. While hope they fix this little problem.