I have not found any official reference to this change anyplace: prior to 7.5.2 the Sage.Entity.Interfaces.IOwner entity contained a RightsCollection collection of user rights (Sage.Entity.Interfaces.IOwnerRights which represents the database table SECRIGHTS).  In 7.5.2 this has changed to now just be called Rights.  If you have any code that was using the previous property name “RightsCollection” you will need to update them when you upgrade to 7.5.2.