When creating a process diagram, I included a call activity and populated the "called element" field in the properties editor.
When I generated the bpmn for the diagram though, the calledElement attribute was missing from that call activity element.
When I close and re-open the bpmn file in the editor, the called element field is still populated in the Properties editor, it is only in the bpmn xml that it is missing.
I also opened an exising bpmn file with the editor which had a call activity. When I generated bpmn for the diagram without making any changes, the calledElement attribute had been removed from the bpmn xml file.