title: setHomeButtonEnabled on PreferenceActivity and nested preference
body: <p>I have preference screen extended <code>PreferenceActivity</code>. For targeting OS 4.0.3, I wanted to add <code>&lt;</code> icon on action bar so I did this in <code>onCreate()</code>.</p>
  
  <pre><code>ActionBar actionBar = getActionBar();
  actionBar.setHomeButtonEnabled(true);
  actionBar.setDisplayHomeAsUpEnabled(true);
  </code></pre>
  
  <p>It worked. <code>&lt;</code> was added to left of app icon. But when I tap the item which goes into the next level (more detail screen), the <code>&lt;</code> won't be displayed. Returning to the top level, the <code>&lt;</code> appears again.</p>
  
  <p>I have never thought about a mechanism of nested preference since smart the <code>PreferenceActivity</code> hides it. Now my question is, why  won't <code>PreferenceActivity</code> display the <code>&lt;</code> on nested preference?</p>
  
  <p>I don't want to argue that I don't need to add <code>&lt;</code> to the preference screen. (Even some of Google's app add, some don't, so I think there is no solid rule for this.)</p>
  
  <p>If there is a simple solution for this, I want to solve this issue.</p>