Valgrind reports this:

==8732== 5236 (52 direct, 5184 indirect) bytes in 1 blocks are definitely lost
in loss record 17625 of 20645
==8732==    at 0x1B909B71: calloc (vg_replace_malloc.c:175)
==8732==    by 0x1C4E8FB7: g_malloc0 (gmem.c:154)
==8732==    by 0x1C4A40D0: g_type_create_instance (gtype.c:1576)
==8732==    by 0x1C48A20F: g_object_constructor (gobject.c:1052)
==8732==    by 0x1C48A861: g_object_newv (gobject.c:949)
==8732==    by 0x1C48B3EA: g_object_new_valist (gobject.c:1033)
==8732==    by 0x1C48B509: g_object_new (gobject.c:830)
==8732==    by 0x1C01C2EB: gdk_pixbuf_new_from_data (gdk-pixbuf-data.c:65)
==8732==    by 0x1C01A832: gdk_pixbuf_new (gdk-pixbuf.c:297)
==8732==    by 0x1C01FFD7: gdk_pixbuf_scale_simple (gdk-pixbuf-scale.c:252)
==8732==    by 0x1B96CA9F: create_normal_cache_icon (nautilus-icon-factory.c:1099)
==8732==    by 0x1B96CCB0: nautilus_icon_factory_get_pixbuf_for_icon_internal
(nautilus-icon-factory.c:1329)
==8732==    by 0x1B96D022: nautilus_icon_factory_get_pixbuf_for_file_internal
(nautilus-icon-factory.c:1545)
==8732==    by 0x80A942A: fm_list_model_get_value (fm-list-model.c:231)
==8732==    by 0x1BE7C310: gtk_tree_model_get_value (gtktreemodel.c:1077)
==8732==    by 0x1BEA5C12: gtk_tree_view_column_cell_set_cell_data
(gtktreeviewcolumn.c:2548)
==8732==    by 0x1BE8FF88: validate_row (gtktreeview.c:4589)
==8732==    by 0x1BE92EAD: validate_visible_area (gtktreeview.c:4866)
==8732==    by 0x1BE9382E: do_presize_handler (gtktreeview.c:5203)
==8732==    by 0x1BE93878: presize_handler_callback (gtktreeview.c:5214)
==8732==    by 0x1C4E4FFF: g_idle_dispatch (gmain.c:3812)
==8732==    by 0x1C4E2E5D: g_main_context_dispatch (gmain.c:1933)
==8732==    by 0x1C4E5C2D: g_main_context_iterate (gmain.c:2564)
==8732==    by 0x1C4E612E: g_main_loop_run (gmain.c:2768)
==8732==    by 0x1BDD0464: gtk_main (gtkmain.c:974)
==8732==    by 0x8070E89: main (nautilus-main.c:434)

It looks like the code in get_icon_from_cache() takes two refs on the icon?

        if (cached_icon == NULL) {
                /* Not in the table, so load the image. */

                /*
                g_print ("cache miss for %s:%s:%s:%d\n",
                         icon, modifier?modifier:"", embedded_text?"<tl>":"",
nominal_size);
                */

                cached_icon = create_normal_cache_icon (icon,
                                                        modifier,
                                                        nominal_size,
                                                        force_nominal);
                /* Try to fallback without modifier */
                if (cached_icon == NULL && modifier != NULL) {
                        cached_icon = create_normal_cache_icon (icon,
                                                                NULL,
                                                                nominal_size,
                                                                force_nominal);
                }

                if (cached_icon == NULL) {
                        cached_icon = factory->fallback_icon;
                        cache_icon_ref (cached_icon);
                }

                /* Create the key and icon for the hash table. */
                key = g_new (CacheKey, 1);
                key->name = g_strdup (icon);
                key->modifier = g_strdup (modifier);
                key->nominal_size = nominal_size;
                key->force_nominal = force_nominal;

                g_hash_table_insert (hash_table, key, cached_icon);
        }

        /* Hand back a ref to the caller. */
        cache_icon_ref (cached_icon);

        /* Since this item was used, keep it in the cache longer. */
        mark_recently_used (&cached_icon->recently_used_node);

        /* Come back later and sweep the cache. */
        nautilus_icon_factory_schedule_sweep (factory);

        return cached_icon;
}