Very strange button movement in LinearLayout about android-flat-button HOT 3 OPEN

<LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="center_vertical"
        android:orientation="horizontal">

        <info.hoang8f.widget.FButton
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="1"/>

        <info.hoang8f.widget.FButton
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="2"/>

        <info.hoang8f.widget.FButton
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:text="3"/>

    </LinearLayout>