Submenus are disabled on Mac OSX with native menu after QMenu::clear()

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
   QMainWindow(parent),
   ui(new Ui::MainWindow)
{
   ui->setupUi(this);

   // Create a submenu with some actions
   subMenu11 = new QMenu("Menu 1.1", this);
   subMenu11->addAction("Action 1");
   subMenu11->addAction("Action 2");
   subMenu11->addAction("Action 3");

   // Create a main menu
   menu1 = new QMenu("Menu 1", this);
   menu1->addMenu(subMenu11);

   menuBar()->addMenu(menu1);

   // Update the main menu before the menu is shown
   connect(menu1, SIGNAL(aboutToShow()), this, SLOT(updateMenu1()));
}

MainWindow::~MainWindow()
{
   delete ui;
}

void MainWindow::updateMenu1()
{
   menu1->clear();
   menu1->addMenu(subMenu11);

   // BUG:
   // With Dev / Qt 5.7 / 5.6 the sub menu 'subMenu11' is now displayed as disabled
   // With Qt 5.5 the sub menu 'subMenu11' was displayed as enabled with
   // the corresponding actions "Action 1", "Action 2", ...
}