title: Weird behaviour with constraints to top / bottom layout guide
body: <p>I've god a storyboard (Xcode 6.4) with a view controller and two subviews arranged vertically over each other. Picture like a Facebook timeline screen in their app, only with just two tiles.</p>
  
  <ul>
  <li>The first view is constrained to the top layout guide, and to the top of the second view below it (distances 8 or whatever).</li>
  <li>The second view is constrained to the bottom of the first view, and to the bottom layout guide (distances 8 or whatever).</li>
  <li>Other horizontal constraints that are not relevant.</li>
  <li>Bottom line - everything is blue and looks great when changing screen types inside storyboard.</li>
  </ul>
  
  <p>While you're expecting the views to be flexible in height and simply scale vertically to fill the whole superview's height, when you run it, something goes wrong.</p>
  
  <p>When running (with simulator or device), on different screens and devices (and iOS versions), you get weird unexpected behaviour near the layout guides, for example a margin shows up between a subview and the relevant top/bottom layout guide.</p>
  
  <p>From what I searched, it looks like an Xcode bug, as I created a clean new project with only these constraints and it still got messed up.</p>