Android : Android PreferenceManager.setDefaultValues trouble

I have a problem with preference default values. I'm trying to set a default value from xml file and then retrieve it. This is my code:

public class MainActivity extends Activity {
int prefValue;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    PreferenceManager.setDefaultValues(this, R.xml.preferences, true);        

    SharedPreferences settings = PreferenceManager.getDefaultSharedPreferences(this);

    prefValue  = settings.getInt("settingValue", 3);
    Log.v("TAGSETT", "p1 "+prefValue);

    Editor editor = settings.edit();
    editor.putInt("settingValue", 25);
    editor.commit();

    prefValue  = settings.getInt("settingValue", 3);
    Log.v("TAGSETT", "p2 "+prefValue);
}

and this is preferences.xml:

<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
    <Preference android:key="settingValue" android:persistent="true" android:defaultValue="10"/>
</PreferenceScreen>

This is the output:

p1 3
p2 25

but in reality I expect this:

p1 10
p2 25

What's wrong? Thanks in advance.