Listview header formatting does not format buttons - android-layout

Question

In a listview a header with two buttons is added. You can see the buttons "none" and "all" below right under the actionbar. Then follows the first item of the list. The buttons should be in the centered and take equal space.
I have a similar solution for a footer (snapshot from a different listview) where it works. You can see the bottom of the list and then the two buttons nicely distributed horizontally.
Here is the code from the header:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:divider="?android:dividerVertical"
android:weightSum="1"
android:showDividers="middle"
android:orientation="horizontal">
<Button
android:id="#+id/btn_none"
style="?android:attr/buttonBarButtonStyle"
android:layout_height="wrap_content"
android:layout_width="0dp"
android:layout_weight="0.5"
android:layout_marginLeft="16"
android:layout_marginRight="16"
android:text="#string/btn_none" />
<Button
android:id="#+id/btn_all"
style="?android:attr/buttonBarButtonStyle"
android:layout_marginLeft="16"
android:layout_marginRight="16"
android:layout_height="wrap_content"
android:layout_width="0dp"
android:layout_weight="0.5"
android:text="#string/btn_all" />
</LinearLayout>
I also tried Relative Layout but again it works only in the footer and not in the header. How can I adjust the buttons in the header?
Here is the footer code. It contains an additional view to establish a horizontal line.
<LinearLayout
android:id="#+id/dts_id_button_bar"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:divider="?android:dividerHorizontal"
android:orientation="vertical"
android:showDividers="middle" >
<View
android:layout_width="match_parent"
android:layout_height="0dp" />
<LinearLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:divider="?android:dividerVertical"
android:orientation="horizontal"
android:showDividers="middle"
android:weightSum="1" >
<Button
android:id="#+id/dts_btn_cancel"
style="?android:attr/buttonBarButtonStyle"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="0.5"
android:text="#string/btn_cancel" />
<Button
android:id="#+id/dts_btn_done"
style="?android:attr/buttonBarButtonStyle"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="0.5"
android:text="#string/btn_done" />
</LinearLayout>
</LinearLayout>