title: defaultValue from xml preference file isn't stored - why?
body: <p>When the application is first startet, I'd like to store all default values I've defined in my prefences.xml by using the 'android:defaultValue' attribute, but some of them are not stored on the device - can someone tell me why?</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  </code></pre>
  
  <p></p>
  
  <pre><code>&lt;PreferenceCategory android:title="@string/prefs_cat_title_x"&gt;
      &lt;ListPreference
          android:key="@string/prefs_key_1"
          android:title="@string/prefs_title_1"
          android:summary="@string/prefs_summary_1"
          android:entries="@array/array1"
          android:entryValues="@array/array1"
          android:defaultValue="@string/prefs_default_1"/&gt;
      &lt;com.myapp.TimePreference
          android:key="@string/prefs_key_2"
          android:title="@string/prefs_title_2"
          android:defaultValue="@string/prefs_default_2"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"/&gt;
      &lt;com.myapp.TimePreference
          android:key="@string/prefs_key_3"
          android:title="@string/prefs_title_3"
          android:defaultValue="@string/prefs_default_3"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"/&gt;
      &lt;ListPreference
          android:key="@string/prefs_key_4"
          android:title="@string/prefs_title_4"
          android:summary="@string/prefs_summary_4"
          android:entries="@array/array2"
          android:entryValues="@array/array2"
          android:defaultValue="@string/prefs_default_4"/&gt;
      &lt;CheckBoxPreference
          android:key="@string/prefs_key_5"
          android:title="@string/prefs_title_5"
          android:summary="@string/prefs_summary_5"
          android:defaultValue="false"/&gt;
      &lt;CheckBoxPreference
          android:key="@string/prefs_key_6"
          android:title="@string/prefs_title_6"
          android:summary="@string/prefs_summary_6"
          android:defaultValue="false"/&gt;
  &lt;/PreferenceCategory&gt;
  
  &lt;PreferenceCategory android:title="@string/prefs_cat_title_common"&gt;
      &lt;com.myapp.DatabaseResetPreference
          android:title="@string/prefs_title_7"
          android:summary="@string/prefs_summary_7"
          android:layout_width="wrap_content"
          android:layout_height="wrap_content"/&gt;
  &lt;/PreferenceCategory&gt;    
  </code></pre>
  
  <p></p>