I have an application with a main window. It opens a find dialog that can remain open, i.e. it is not modal. I mark it as STAY_ON_TOP so it does not disappear behind the application window.
The application pops up a message box to announce that the search term cannot be found, but it CANNOT BE SEEN because it is located behind the find dialog. I can’t even move the find dialog out of the way because the message box is modal, so I cannot transfer focus to the find dialog. The only way out of the dilemma is to blindly press a key – space bar, escape, etc. – that dismisses the message box.
So after more than 20 years of development, Windows is still too stupid to realise that it is presenting an invisible modal dialog to the user.