We had this issue in one of our projects where in the Artifact Links section of a User Story a list of tasks that were associated were displayed. However in Artifact Links section of those Tasks there was the User Story. This caused the User Story not to be displayed in the Sprint Plan and of course the card wall. A lot of time was spent trouble shooting the issue as looking at the Release, Epic, Sprint and User Story all the Artifact Links seemed to be correct. The circular reference in the Artifacts Links caused a problem.

In order to avoid this problem in the future, I propose that Tuleap implement something similar to what has been done in Bugzilla and Collabnet TeamForge (see attachments)