QShortcut fires multiple times when WebEngine used on macOS

Apply the attached patch to simplebrowser and observe multiple lines of output when the 's' key is pressed. Event appears to fire only once on a different example program that doesn't use WebEngine. This didn't happen in 5.9, and doesn't happen on Linux, so it appears to be a regression on macOS.

 --- simplebrowser-orig/browserwindow.cpp 2017-11-29 18:42:28.000000000 +1000
+++ simplebrowser/browserwindow.cpp 2017-12-14 15:10:58.000000000 +1000
@@ -66,6 +66,7 @@
#include <QToolBar>
#include <QVBoxLayout>
#include <QWebEngineProfile>
+#include <QShortcut>

BrowserWindow::BrowserWindow(Browser *browser, QWebEngineProfile *profile)
: m_browser(browser)
@@ -91,6 +92,11 @@
menuBar()->addMenu(createWindowMenu(m_tabWidget));
menuBar()->addMenu(createHelpMenu());

+ QShortcut *scut = new QShortcut(QKeySequence("s"), this);
+ connect(scut, &QShortcut::activated, [this]()

);
+
QWidget *centralWidget = new QWidget(this);
QVBoxLayout *layout = new QVBoxLayout;
layout->setSpacing(0);