QSplashScreen and QLabel not painting correctly on Linux

QLabel and QSplashScreen share the same problem of not painting when needed on Linux although they behave perfectly on Windows.  For a QLabel calling QApplication::processEvents() should cause it to paint immediately. For QSplashScreen calling repaint() should cause it to paint immediately because it calls processEvents() internally.

Attached is demo code using QSplashScreen (however the behaviour would be the same if using QLabel) If run on Windows, the window is painted and you see the message "You should see this" immediately. When run on Linux the message is not displayed until 10 seconds later when the demo method Test::lengthyProcess() completes.