title: git auto-merge does not work as expected
body: <p>I happen to have a file (say <strong>abc</strong>) in two branches: <em>master</em> and <em>sample</em>. </p>
  
  <p>The commit date for <strong>abc</strong> on <em>sample</em> is older than <strong>abc</strong> on current <em>master</em>; in other words <strong>abc</strong> is latest on <em>master</em>. </p>
  
  <p>Now, I ran:</p>
  
  <pre><code>git checkout sample
  git merge master 
  </code></pre>
  
  <p>It auto-merged several files (including <strong>abc</strong>).</p>
  
  <p>Problem: Line#42 in <strong>abc</strong> seems to persist from branch <em>sample</em> instead getting replaced from <em>master</em>. </p>
  
  <p>Why is this happening ? I was quite expecting otherwise. Please help. </p>