Details
Major Description
Property Sets with no 'key' field have auto-generated keys given to each instance each time an update is made on the category that contains the property set definition.
When instances are deleted, previous autogenerated keys are not reused so that each instance can have it's key changed. Its a problem if there is a reference to this instance stored somewhere (a Property of type PROPERTY_SET, or the last sent date property in report plugin.
We should reuse the keys and give new keys only to new instances
