The fade effect is being false triggered when switching between virtual
desktops. These false triggers cause window flickering(see video below),
which is really annoying sometimes.
As temporal countermeasure, ignore windowShown/windowHidden signals.
Ignoring previously mentioned signals won't change Plasma experience too
much, e.g. tooltips/default application launcher/etc still would fade in/out.
(I think they don't reuse the same window)
This is a little bit radical change, but currently the fade effect does more harm than good...