ComboBox: binding loop for Material.foreground

<Unknown File>: QML : Binding loop detected for property "foreground"
<Unknown File>: QML : Binding loop detected for property "foreground"

import QtQuick 2.6
import QtQuick.Controls 2.0
import QtQuick.Controls.Material 2.0

ApplicationWindow {
    visible: true
    width: 640
    height: 480

    header: ToolBar {
        Row {
            spacing: 20
            ComboBox {
                model: ["Light"]
            }
            ComboBox {
                flat: true
                model: ["Flat Light"]
            }
            ComboBox {
                model: ["Dark"]
                Material.theme: Material.Dark // <==
            }
            ComboBox {
                flat: true
                model: ["Flat Dark"]
                Material.theme: Material.Dark
            }
        }
    }

    Row {
        anchors.centerIn: parent
        Pane {
            Column {
                spacing: 20
                ComboBox {
                    model: ["Light"]
                }
                ComboBox {
                    flat: true
                    model: ["Flat Light"]
                }
            }
        }
        Pane {
            Material.theme: Material.Dark
            Column {
                spacing: 20
                ComboBox { // <==
                    model: ["Dark"]
                }
                ComboBox {
                    flat: true
                    model: ["Flat Dark"]
                }
            }
        }
    }
}

Material.foreground: Material.foreground === Material.toolTextColor ? undefined : Material.foreground

Material.foreground: flat ? undefined : Material.foreground