When user create relationship from parent entity to child, attributes from parent entity are migrated to child. When this relation is deleted, attributes are deleted too. It would be nice have some possibility to change this behavior. For example chechbox on attribute form "Keep Attribute", when will be enable and checked when attribute is migrated. In this case user can uncheck and attribute preserver after delete relationship.
Source:
http://www.toadworld.com/products/toad-data-modeler/f/30/t/32306