Can't open platform context menu from MouseArea's onPressed handler on Ubuntu 16.04

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

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

    MouseArea {
        anchors.fill: parent
        acceptedButtons: Qt.RightButton
        // Doesn't work
        onPressed: contextMenu.open()
        // Works
//        onClicked: contextMenu.open()
    }

    Menu {
        id: contextMenu

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