GtkExpander seems broken when expanded manually

gtk-expander-set-expanded.c

/*
 * Compile with:
 * gcc $(pkg-config --cflags gtk+-3.0 --libs gtk+-3.0) -lm *.c
 */

#include <stdlib.h>
#include <glib.h>
#include <gtk/gtk.h>

#define EXPANDED
//#undef EXPANDED

int
main(int argc, char *argv[])
{
	/* Init */
	gtk_init(&argc, &argv);

	/* Create a clickable label */
	GtkWidget *label;
	label = gtk_label_new("<b><a href=\"https://developer.gnome.org/gtk3/\">GTK+3</a></b>");
	gtk_label_set_use_markup(GTK_LABEL(label), TRUE);

	/* Create an expander that holds the label */
	GtkWidget *expander;
	expander = gtk_expander_new("Expandable");
	gtk_container_add(GTK_CONTAINER(expander), label);

	/* Create the main window that holds the expander */
	GtkWidget *window;
	window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
	gtk_container_add(GTK_CONTAINER(window), expander);

#ifdef EXPANDED
	/* Expand - this is where things seem bogus */
	gtk_expander_set_expanded(GTK_EXPANDER(expander), TRUE);
#endif

	/* Main loop */
	gtk_widget_show_all(window);
	gtk_main();

	return EXIT_SUCCESS;
}