Context menu opens further away from the cursor the further the mouse is clicked from the top-left edge of the window

import QtQuick 2.8
import QtQuick.Window 2.2
import Qt.labs.platform 1.0

Window {
    id: window
    width: 400
    height: 400
    visible: true

    TextEdit {
        id: editor
        anchors.fill: parent

        MouseArea {
            anchors.fill: parent
            acceptedButtons: Qt.RightButton
            onClicked: contextMenu.open()
        }

        Menu {
            id: contextMenu

            MenuItem {
                text: qsTr("Copy")
            }
            MenuItem {
                text: qsTr("Cut")
            }
            MenuItem {
                text: qsTr("Paste")
            }
        }
    }
}