Strange problem I’ll be short.
I can shutdown / reboot the system from KDE Menu.
I can’t do the same with GNome menu. It just logs me out to Welcome Screen if I hit Shutdown or Restart from the Window in GNome.
I chose my default desktop as KDE but also installed Gnome alongside. Installed from DVD and also made my user a member of the wheel group, un-commenting the line in visudo.