==8732== 19 bytes in 1 blocks are definitely lost in loss record 8215 of 20645
==8732==    at 0x1B909222: malloc (vg_replace_malloc.c:130)
==8732==    by 0x1C4E8F55: g_malloc (gmem.c:137)
==8732==    by 0x1C4F9531: g_strdup (gstrfuncs.c:91)
==8732==    by 0x1BA334BA: eel_mime_application_chooser_new
(eel-mime-application-chooser.c:505)
==8732==    by 0x80A4B16: is_directory_ready_callback (fm-properties-window.c:3345)
==8732==    by 0x1B939D32: ready_callback_call (nautilus-directory-async.c:1262)
==8732==    by 0x1B93B29F: nautilus_directory_async_state_changed
(nautilus-directory-async.c:1854)
==8732==    by 0x1B93DA9D: nautilus_directory_call_when_ready_internal
(nautilus-directory-async.c:1344)
==8732==    by 0x1B97A3C9: vfs_file_call_when_ready (nautilus-vfs-file.c:66)
==8732==    by 0x1B953A4F: nautilus_file_call_when_ready (nautilus-file.c:5455)
==8732==    by 0x80A528F: fm_properties_window_present (fm-properties-window.c:3697)
==8732==    by 0x8087115: action_properties_callback (fm-directory-view.c:1150)
==8732==    by 0x1C4914AC: g_cclosure_marshal_VOID__VOID (gmarshal.c:77)
==8732==    by 0x1C4852FB: g_closure_invoke (gclosure.c:437)
==8732==    by 0x1C494A7E: signal_emit_unlocked_R (gsignal.c:2488)
==8732==    by 0x1C49605A: g_signal_emit_valist (gsignal.c:2247)
==8732==    by 0x1C4963E2: g_signal_emit (gsignal.c:2291)
==8732==    by 0x1BD03D09: _gtk_action_emit_activate (gtkaction.c:1038)
==8732==    by 0x1BD041E8: gtk_action_activate (gtkaction.c:1065)
==8732==    by 0x1C4914AC: g_cclosure_marshal_VOID__VOID (gmarshal.c:77)
==8732==    by 0x1C4852FB: g_closure_invoke (gclosure.c:437)
==8732==    by 0x1C494A7E: signal_emit_unlocked_R (gsignal.c:2488)
==8732==    by 0x1C49605A: g_signal_emit_valist (gsignal.c:2247)
==8732==    by 0x1C4963E2: g_signal_emit (gsignal.c:2291)
==8732==    by 0x1BEB369D: gtk_widget_activate (gtkwidget.c:3734)
==8732==    by 0x1BDE2AD0: gtk_menu_shell_activate_item (gtkmenushell.c:1034)
==8732==    by 0x1BDE2D95: gtk_menu_shell_button_release (gtkmenushell.c:640)
==8732==    by 0x1BDD81F1: gtk_menu_button_release (gtkmenu.c:2567)
==8732==    by 0x1BDD236C: _gtk_marshal_BOOLEAN__BOXED (gtkmarshalers.c:83)
==8732==    by 0x1C484E28: g_type_class_meta_marshal (gclosure.c:514)

Seems details->real_mime_type is not being freed in the ->finalize method?