title: iOS8 - constraints ambiguously suggest a height of zero
body: <p>Has anyone got any idea how to debug this?</p>
  
  <blockquote>
    <p>Warning once only: Detected a case where constraints ambiguously suggest a height of zero for a tableview cell's content view. We're considering the collapse unintentional and using standard height instead.</p>
  </blockquote>
  
  <p>The rows have a fixed height as set by</p>
  
  <pre><code>- (CGFloat)tableView:(UITableView *)tableView 
             heightForRowAtIndexPath:(NSIndexPath *)indexPath{
     return 34.0;
  }
  </code></pre>
  
  <p>And all the <code>constraints</code> seem to be happy...</p>