Dialog is closed when releasing a drag outside of it

import QtQuick 2.8
import QtQuick.Controls 2.1
import QtQuick.Layouts 1.3

ApplicationWindow {
    id: window
    objectName: "window"
    width: 800
    height: 800
    visible: true

    Button {
        id: button
        text: "Open"
        onClicked: dialog.open()
    }

    Dialog {
        id: dialog
        objectName: "texturedFillSettingsDialog"
        title: qsTr("Textured Fill settings")
        // Doesn't work if these are specified
        x: Math.round(parent.width - width) / 2
        y: Math.round(parent.height - height) / 2
        modal: true
        dim: false
        focus: true
        closePolicy: Popup.CloseOnEscape | Popup.CloseOnReleaseOutside

        contentItem: RangeSlider {
            id: root
            from: -1
            to: 1
            first.value: 0.25
            second.value: 0.75
            objectName: "hueVarianceSlider"

            Layout.fillWidth: true
        }
    }
}