DEBUGGED AND DIAGNOSED 2015-08-04. A bug showed up in the Landscapes DB which I think is generic: when a record contains two different one-to-many fields which link to the same table at one remove, editing a record can result in the creation of more links than should be created. It looks as though for each table which is linked through the same set of foreign keys, a new entry is created, causing there to be links that did not previously exist, generated through the save operation. This must be fixed. I've worked around it by removing one of the links in the owners table in that db (to sellers).