Zenity title bar will not appear when using zenity within /etc/gdm/PreSession/Default script

Issue

• When a Zenity window is executed from the /etc/gdm/PreSession/Default script, the --text, --cancel-label, and --ok-label options work fine, but there is no title on the dialog box displayed.
  • The same command can be pasted into a Bourne (sh) shell window and executed fine, with the window title showing.
  • Manually executing the zenity command in a terminal gives the desired result.