There is apparently multiple issues to handle there:
1. When creating a CR for a new diagram, 2 different CRs are created and if the users has rights, the page is also created (even with save as CR). The attachments are only pushed in the created doc, and not in the CRs at all. And one of the CR is missing the diagram xobject
2. Apparently there is a bug when getDefaultDocumentEditor is called: the document used for checking for sheets doesn't seem to be the modified document