Gtk application dies when certain gb18030 character are used.

I've encoded one of these chars to utf16 in order to show the bug.
The only pattern I found was that those char that causes gtk to die are
encoded in 3 bytes when g_utf16_to_utf8 is used.
For chars that are encode in 2 bytes in UTF-8 the problem doesn't happens.
(I've used the items_written param of g_utf16_to_utf8 to check this);

I believe the conversion process is Ok though.
Be sure that the locale of your machine is set to gb18030 before running
the test code.

Here is my Test Code:

#include <gtk/gtk.h>

int main (int argc, char** argv) {
	GtkWidget *shellHandle, *textHandle;
   	gunichar2 buffer[] = {'a', 0xfb4e, 'b'};  //doesn't works
//   	gunichar2 buffer[] = {'a', 0x628, 'b'};   //works
	gchar* utf8;

        gtk_init_check (&argc, &argv);
	shellHandle = gtk_window_new (GTK_WINDOW_TOPLEVEL);
	textHandle  = gtk_entry_new();
	gtk_container_add (GTK_CONTAINER (shellHandle), textHandle);

	utf8 = g_utf16_to_utf8 (buffer, 3, NULL, NULL, NULL);
	gtk_entry_set_text (GTK_ENTRY(textHandle), utf8);
	g_free (utf8);
	g_signal_connect (G_OBJECT (shellHandle), "destroy", G_CALLBACK
(gtk_main_quit), NULL);
	g_signal_connect (G_OBJECT (shellHandle), "delete_event",G_CALLBACK
(gtk_main_quit), NULL);
	gtk_widget_show_all (shellHandle);
	gtk_main();

}