Crash with UpdateWindowTitle event triggered by closing a dialog (mac)

We hit this crash after upgrading Qt base from 5.10.0 to 5.15.4. It happens intermittently. The call stack we have captured looks like:

1 libQt5Qml.5.15.4.dylib!QQmlData::isSignalConnected(QAbstractDeclarativeData*, QObject const*, int)
2 libQt5Core.5.15.4.dylib!void doActivate<false>(QObject*, int, void**)
3 libQt5Widgets.5.15.4.dylib!QWidget::setWindowTitle(String const&)
...
6 libQt5Core.5.15.4.dylib!void doActivate<false>(QObject*, int, void**)
...
10 libQt5Widgets.5.15.4.dylib!QApplicationPrivate::notify_helper(QObject*, QEvent*)
11 libQt5Widgets.5.15.4.dylib!QApplication::notify(QObject*, QEvent*)
...
13 libQt5Core.5.15.4.dylib!QCoreApplication::notifyInternal2(QObject*, QEvent*)
14 libQt5Core.5.15.4.dylib!QCoreApplicationPrivate::sendPostedEvents(QObject*, int, QThreadData*)
15 libqcocoa.dylib!QCocoaEventDispatcherPrivate::processPostedEvents()
16 libqcocoa.dylib!QCocoaEventDispatcher::processEvents(QFlags<QEventLoop::ProcessEventsFlag>)
17 libtabcore.dylib!CancelMgr::WaitForSignal(IEvent... >)
...
20 libQt5Core.5.15.4.dylib!QObjectPrivate::deleteChildren()
21 libQt5Widgets.5.15.4.dylib!Widget::~QWidget()
22 libtabui.dylib!ConnectWebDataDialog::ShowWebDataDialog(...)
... ... 

We don't use the QML; but the union in QtBase - src/corelib/kernel/qobject_p.h

union

Unknown macro: { QObject *currentChildBeingDeleted; // should only be used when QObjectData}

;

could lead the code to QmlData::isSignalConnected...

Attached is a Qt creator project - WindowTitleDialogIssue.zip - for easy repro.