Oh my God, I can't beleive it. I solved my problem just setting the ID of the fragment that was having problem.
Now, the XML's layout of the Activity is like this:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<fragment
android:name="com.soongz.ui.fragment.ListaDeMusicasFragment"
android:id="@+id/lista_de_musicas_fragment"
style="?layoutListViewMusicas" />
<fragment
android:id="@+id/player_reduzido_fragment"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:name="com.soongz.ui.fragment.PlayerReduzidoFragment"/>
</LinearLayout>
I don't know why. It must be a bug.