title: In Python (or Mac OS): two different files recognized as same file and gets re-written
body: <p>Simplified description of problem, I have:</p>
  
  <p>dir and file structure:</p>
  
  <pre><code>./top.py
  ./Task/Task.py   (was deleted and then renamed as:)
  ./Task/task.py
  </code></pre>
  
  <p><code>top.py</code> import <code>task.py</code>. But then when I run <code>top.py</code>, I saw that the <code>task.py</code> automatically changed to <code>Task.py</code>. </p>
  
  <p>Why is this happening?</p>
  
  <p>(I use mvim as the editor on Mac OS 10.6.)</p>