title: onSharedPreferenceChanged not fired all the time
body: <p>I have a weird problem with this method. It's called, when i edit a EditTextPreference, only when i change the value, and on a MultiSelectListPreference only the first time i change.
  This is my fragment code.</p>
  
  <pre><code>public class PrefFragment extends PreferenceFragment implements OnSharedPreferenceChangeListener {
      @Override
      public void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setRetainInstance(true);
          addPreferencesFromResource(R.xml.my_preferences);
      }
  
      @Override
      public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
          // DO STUFF
      }
  
      @Override
      public boolean onPreferenceTreeClick(final PreferenceScreen preferenceScreen, final Preference preference) {
          // TODO Auto-generated method stub
          super.onPreferenceTreeClick(preferenceScreen, preference);
          // DO STUFF
  
      }
  
      @Override
      public void onResume() {
          super.onResume();
          // Set up a listener whenever a key changes
          getPreferenceManager().getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
      }
  
      @Override
      public void onPause() {
          super.onPause();
          // Unregister the listener whenever a key changes
          getPreferenceManager().getSharedPreferences().unregisterOnSharedPreferenceChangeListener(this);
      }
  }
  </code></pre>
  
  <p>and this is my_preferences.xml file</p>
  
  <p><pre>
  </p>
  
  <code>&lt;PreferenceCategory android:title="Title1" &gt;
      &lt;EditTextPreference
          android:dialogMessage="@string/pref_pers_1_msg"
          android:dialogTitle="@string/pref_pers_1"
          android:key="@string/pref_pers_1_key"
          android:title="@string/pref_pers_1" /&gt;        
     &lt;EditTextPreference
          android:dialogMessage="@string/pref_pers_2_msg"
          android:dialogTitle="@string/pref_pers_2"
          android:key="@string/pref_pers_2_key"
          android:title="@string/pref_pers_2" /&gt;        
     &lt;EditTextPreference
          android:dialogMessage="@string/pref_pers_3_msg"
          android:dialogTitle="@string/pref_pers_3"
          android:key="@string/pref_pers_3_key"
          android:title="@string/pref_pers_3" /&gt;
  &lt;/PreferenceCategory&gt;
  &lt;PreferenceCategory android:title="Title2" &gt;
       &lt;MultiSelectListPreference
          android:dialogTitle="title_dialog"
          android:entries="@array/array"
          android:entryValues="@array/array_elements"
          android:key="pref_pers_4"
          android:title="Title2" /&gt;
  &lt;/PreferenceCategory&gt;
  </code></pre>
  
  <p></p>