Create a directory structure c:\test\folder1\folder2 and run the example below. Try to delete "folder1" in explorer. This is not possible, Explorer complains about Access Denied, and none of the folders will be deleted. However, QFileSystemWatcher will emit directoryChanged("c:\test\folder1\folder2") at least once, and in some cases even endlessly. Some times the folders end up being deleted - all in all the behavior is rather unpredictable.
Half of the time, debug output "QFileSystemWatcher: FindNextChangeNotification failed (Access is denied.)" is generated.
However it's a native Windows behaviour - these problems are there even with the example application from the MSDN.