I know of the little clip you speak of. I'm actually not sure of what it does but speculation says it could be something as simple as a ground or as amazing as a point of contact which turns the entire back piece into an antenna. I'm going out on a limb and say that it's probably just a ground. From your issue, it sounds like when you're sliding that back piece on it causes your phone to shut off. Have you ensured that the little metal piece is not making contact with another component it's not supposed to? Try taking the battery connector off and place the metal piece down first then reinstall the battery connector. If its installed properly, then some other components could be touching the metal back. Look for signs of scraps or marks that could indicate it. Anyways, I'm just making a suggestion. I hope you get your issue resolved.