title: Blender - Intersection between 2 objects deletes part of my first object
body: <p>I'm making a chess piece (a bishop) and I am trying to make the top notch.
  For this purpose, I made a new cube, resized it and put on the place to make the cut.</p>
  
  <p>I want to make a cut using a modifier: Boolean, intersecting the two objects.</p>
  
  <p>The problem I am facing is that while intersecting, the top UV Sphere that simulates the 'hat' of the bishop disappears.
  What I did so far:
  - Remove Doubles
  - CTRL+J to join Bishop+Hat(UV Sphere) to make 1 component</p>
  
  <p>Nothing helped and when trying to intersect, the UVSphere-hat disappears.</p>
  
  <p>Why? How to solve?</p>
  
  <p>Here is the bishop before modifier, with hat:
  Here is the .blend file to catch the problem faster:
  Thank you for your help :-)</p>