When a messagebox appears after closing a mainwindow after dismissing a messagebox then it can cause a crash

When a messagebox appears after closing a mainwindow after dismissing a messagebox then it can cause a crash.

With the attached example, do the following:

• Start the application and dismiss the initial messagebox.
• Make sure the window is big enough to contain a whole messagebox
• Type something and then click on the red X to close the window
• Choose Don't Save
• Go to File | New

then it will crash right away.