title: Matplotlib ignoring timezone
body: <p>The following plot </p>
  
  <pre><code>import matplotlib
  f= plt.figure(figsize=(12,4))
  ax = f.add_subplot(111)
  df.set_index('timestamp')['values'].plot(ax=ax)
  ax.xaxis.set_major_locator(matplotlib.dates.HourLocator(interval=1))
  ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter('%I'))
  plt.show()
  </code></pre>
  
  <p>Renders the hour in the wrong zone (GMT) even though I have:</p>
  
  <pre><code>&gt; df['timestamp'][0]
  Timestamp('2014-09-02 18:37:00-0400', tz='US/Eastern')
  </code></pre>
  
  <p>As a matter of fact, if I comment out the line:</p>
  
  <pre><code>ax.xaxis.set_major_formatter(matplotlib.dates.DateFormatter('%I'))
  </code></pre>
  
  <p>the hour is rendered in the right time zone. </p>
  
  <p>Why?</p>