Gtk::Builder and Gtk::FontChooserDialog

[Phil Wolff <adiabat centurylink net>]

When calling Gtk::Builder::get_widget () on a Gtk::FontChooserDialog 
specified in Glade as a top-level window, this warning is issued:

    gtkmm-WARNING **: gtkmm: Attempt to call Gtk::manage() on a 
Gtk::Window, but a Gtk::Window has no parent container to manage its 
lifetime.

While this is certainly true, the warning doesn't appear for similar 
instances of Gtk::AboutDialog or Gtk::ColorChooserDialog. Is there 
something special about the FontChooserDialog that warrants the warning?