Reposting because previous report (1775) was not initially reported with full information, and was therefore mis-classified as documentation rather than bug, and left unassigned.
If a Collection object is given the RELS_EXT relationship isMemberOf itself, it causes infinite loops, evidenced in the breadcrumbs generated on such an object. This can cause major problems depending on configuration.
Example: collection object "Newsletter Archives" was (accidentally) made a member of itself, resulting in this set of breadcrumbs:
"Home › Browse all collections › ... › Newsletter Archives › Newsletter Archives › Newsletter Archives › Newsletter Archives › Newsletter Archives › Newsletter Archives › Newsletter Archives › Newsletter Archives › Newsletter Archives › Newsletter Archives"
This looping relationship issue could have larger implications than breadcrumbs depending on settings - see ticket #1774, where the looping causes a Solr crash.
Proposing that users be blocked from making a collection a member of itself. When the collection membership is set, a check should run to make sure that the isMemberOf relationship is not to itself. On failing the check, setting the relationship should fail and return the error message, "A collection cannot be a member of itself" or something to that effect.
Investigation (see comments in 1775) reveals that this ONLY occurs when an object is directly made isMemberOf itself. Longer chain relationships (e.g. collection1 isMemberOf collection2 and collection3; collection2 isMemberOf collection 3) cause no problems. Therefore, a simple check on collection membership assignment would resolve the issue.