Mouse messages for QDockWidget are incorrectly cast to QMainWindow causing a crash

My app uses multiple floating QDockWidgets.  When they are combined, a crash occurs.

I will walk through the stack since I am unable to create a repro case.

See the video for how crash is reproduced.

Here is the complete stack

It is a mouse event

Farther down we sent event to the receiver

The receiver is QDockWidgetGroupWindow

 

QDockWidgetGroupWindow treats it as a windowEvent

Which is handled by QMainWindowLayoutSeparatorHelper as a HoverMove and adjustCursor is called

adjustCursor call findSeparator

Which calls toolBarAreaLayout

 

 

At this point, you can see that mainWindow is derived from QDockWidgetGroupWindow

Now we cast the parentWidget to QMainWindow, when it is not a QMainWindow

        auto mainWindow = static_cast<QMainWindow>(parentWidget());

After this, it crashes.  'd' is not valid after this cast

QMainWindowLayout *qt_mainwindow_layout(const QMainWindow *mainWindow)

{     return QMainWindowPrivate::mainWindowLayout(mainWindow); }

 

    static inline QMainWindowLayout *mainWindowLayout(const QMainWindow *mainWindow)
   

{         return mainWindow ? mainWindow->d_func()->layout.data() : static_cast<QMainWindowLayout *>(nullptr);     }