This trophy is not buggy, it happens that you can not be touched in any way by any zed, do not be touched or touch any zed. the trophy is definitely not buggy, do a whole mission without being touched, that surely the trophy will be unlocked. It will not be easy to pass a phase without being touched, but it is possible after many attempts, decorate the respaw of the zeds, look for the best place to kill the zeds. the map I used to win the trophy was the farmhouse. Sorry for any errors with my English my friends, I'm Brazilian I do not understand English, I'm using Google translator. Good luck, I hope you all succeed.