i saw that exact thing earlier. i was an ally with a sniper rifle and i saw what appeared to be a frozen character with a sniper rifle. i dont see an allied icon above his head or anything when i'm standing right by him so i try pistol whipping him. nothing. try shooting, goes right through him. i'm not sure if that was me or not, but it was damn strange. i havent had a hostile experience with one yet. sounds like a bug those guys have figured out how to reproduce