How to add an usecase to a system in an usecase diagram

Plug-in & Open API
1

I’m creating a usecase diagram and wanted to add usecase to an before created system
basicly:

private void testUseCase() {
        ISystem system = getFactory().createSystem();
        //more..
        IUseCase useCase = getFactory().createUseCase();
        //more..
        IDiagramElement systemDiagramElement = getDiagramManager().createDiagramElement(getDiagram(), system);
        IDiagramElement useCaseDiagramElement = getDiagramManager().createDiagramElement(getDiagram(), useCase);
        
        systemDiagramElement.setModelElement(system);
        useCaseDiagramElement.setModelElement(useCase);
        
        systemDiagramElement.addChild((IShapeUIModel)useCaseDiagramElement);   
    }

when running the plugin the elements are displayed, but the usecase isn’t a child of the system.

althougt it’s listed proper in the diagram navigator

any idea how to get the usecase displayed “in” the system?so if you move the system the usecase is draged automatically.

kind regards,

klm