When the artifact and art keywords are defined as belonging to Tracker v3 realm:

mysql> select keyword, service_short_name, nature, link from reference where scope = 'S' and keyword in ('art', 'artifact');
+----------+--------------------+----------+-------------------------------------------------+
| keyword  | service_short_name | nature   | link                                            |
+----------+--------------------+----------+-------------------------------------------------+
| art      | tracker            | artifact | /tracker/?func=detail&aid=$1&group_id=$group_id |
| artifact | tracker            | artifact | /tracker/?func=detail&aid=$1&group_id=$group_id |
+----------+--------------------+----------+-------------------------------------------------+
2 rows in set (0.00 sec)

The cross references across projects are not properly stored and then doesn't appear in UI.