The force ghost scene is an easy target to manipulate after George massicared it in the SEs.
Although maybe a force ghost may be only visible to a Jedi who has had a direct link with a fallen Jedi. Yoda may have been able to talk to Maces force ghost in Empire but Luke wouldnt be able to see him (in the same way Leia couldnt see the force ghosts at the end of Jedi).
Wait, what?