Version: unspecified (using KDE 4.4.4)
Other DEs such as XFCE and GNOME now use ConsoleKit instead of XDMCP to request shutdown/restart on logout, so these logout types just return the user to KDM.
Steps to Reproduce:
Shutdown from GNOME's logout dialog
Return to KDM greeter
System shuts down
complementary to bug 186198.
i'm not sure what kdm is supposed to have to do with that - i see no indication that consolekit asks the display manager to do the actual shutdown.
fwiw, this has so totally nothing to do with xdmcp ...
KDM is unmaintained and not used in KDE Plasma 5.
SDDM is the login manager used in KDE Plasma 5. If you still have this same issue with SDDM, please file an issue on the SDDM bugtracker (after doing a search for existing issues first!): https://github.com/sddm/sddm/issues/