Bug#785691: Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.

[Pheeble]

This is not a 'bug' as such.

One of the GTK+ devs decided to insert this warning into the Gtk Dialog 
function gtk_dialog_map because he thinks no dialog window (as used by 
LOTS of applications, including Zenity) should run without a parent 
window - see 
https://mail.gnome.org/archives/commits-list/2014-May/msg00576.html and 
https://github.com/GNOME/gtk/blob/master/gtk/gtkdialog.c.

Or perhaps it is a bug - in Gtk+.