when gparted is started from the menu via gksu-polkit the path is set to /usr/local/bin:/bin:/usr/bin
ntfsprogs for example used by gparted are in /usr/sbin
to be able to detect the the PATH needs to include at least /usr/sbin
i don't know where this should be fixed. ideally a policy file for gparted would be created which sets the PATH
(is that possible? running gksu-polkit xterm; gives a different path, so there must be something setting that).
alternatively a workaround would be to manually fix the PATH in the /usr/bin/gparted script