reproducible with 061010, regression

steps:
1. create java platform model
2. add package with scoped activity diagram
3. add two invocations to the diagram
activity diagram is shown in navigator correctly
4. add class diagram to the project
5. add several classes to the diagram
class diagram is shown correctly
6. activate activity diagram
navigator shows class diagram
7. add several elemnts to activity diagram
navigator is refreshed with class diagram