Fixing an EOModel layout in Xcode

I created an EOModel in Xcode, created two entities, which I then deleted. I then opened the model in EOModeler, finished all the attributes and some of the relationships. I want to finish the relationships in Xcode, but on reopening it in Xcode, while all the entities and attributes are there, the diagram is essentially blank, with only 2 empty, unconnected entities. Any ideas how to fix this?