So on my 15" Macbook Pro, I got the hard shell protector that they sell in the Mac store. There is a piece for the top, and the bottom. Well, when I open it, once the screen flips back to a certain point, the top part of the shell "catches" (for lack of a better word) a little bit, so that you feel a little "bump" in the opening. Is that normal? I do not want undue wear and tear.