Bottom area layout reduction

flashcard.xml

    <LinearLayout
        android:id="@id/bottom_area_layout"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:orientation="vertical" >

        <!-- Buttons -->
        <LinearLayout <!-- NOTE: everything works fine if this LinearLayout is removed -->
            android:id="@+id/flashcard_layout_flip"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:orientation="vertical" >

            <Button
                android:id="@+id/flip_card"
                style="?android:attr/buttonStyleSmall"
                android:layout_width="fill_parent"
                android:layout_height="15sp"
                android:background="@color/blue"
                android:lines="1"
                android:text="@string/show_answer" />
        </LinearLayout>
    </LinearLayout>