Glib::Type->list_ancestors on enum or flags

[Kevin Ryde <user42 zip com au>]

The program

    use strict;
    use warnings;
    use Gtk2 '-init';
    my $type = 'Gtk2::Gdk::CursorType';
    # my $type = 'Gtk2::Gdk::EventMask';
    print Glib::Type->list_ancestors ($type),"\n";

gets an error

    problem looking up parent package name, gtype 48 at foo.pl line 8.

or with EventMask instead of CursorType,

    problem looking up parent package name, gtype 52 at foo.pl line 8.

Those gtypes 48 and 52 are G_TYPE_ENUM and G_TYPE_FLAGS.  Are they
supposed to be able to come out as, I guess, Glib::Enum and Glib::Flags?
Or is it a case of don't do that?