The import is most likely working. There is no common language used to describe the actual ‘diagrams’ that UML designers use, the only consistent standard is a language used to describe the model, that is XMI. So what you need to do after importing, is switch to your different types of model view (Class outline for example) then drag and drop from your model onto the diagram. I realize this is confusing, if you two want to share diagrams, sharing the UMR file is going to allow you to keep the diagrams themselves and not just the model def.