QML ColorDialog ignores flags

import QtQuick.Controls
import QtQuick.Dialogs

ApplicationWindow {
    visible: true
    Button {
        text: color_dialog.selectedColor
        anchors.centerIn: parent
        ColorDialog {
            id: color_dialog
            flags: ColorDialog.ShowAlphaChannel | ColorDialog.NoButtons // XXX no effect
        }
        onClicked: color_dialog.open()
    }
}