Run the qtbase/examples/widgets/mainwindows/mainwindow example

Right click on the white area in the middle, you will get a popup menu with Copy and Paste, both disabled (even though the application doesn't try to put them there)

Now you can't do anything else without crashing the app: click outside the menu, click on it, click the titlebar etc.

I was actually trying to find out if action shortcuts on popup menus can work, but this is much worse.