Bug 123207 PropertyHandle items cannot be moved down
Use the property handle to move down the item. It seems not work.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/internal/ui/dialogs/PropertyHandleTableViewer.java
btnDown = new Button(btnComposite, SWT.ARROW | SWT.DOWN);
            btnDown.setLayoutData(btnData);
            btnDown.addSelectionListener(new SelectionListener(){
                public void widgetSelected(SelectionEvent e)
                {
                    
                    int index = viewer.getTable( ).getSelectionIndex( );
                    PropertyHandle handle = (PropertyHandle) viewer.getInput();
                    if ( index > -1
                            && handle.getListValue( ) != null
                            && index < handle.getListValue( ).size( ) - 1)
                    {
                        viewer.cancelEditing();
                        try
                        {
                            handle.moveItem( index, index + 2 );
                        }
                        catch ( PropertyValueException e1 )
                        {
                            ExceptionHandler.handle( e1 );
                        }
                        viewer.refresh( );
                        viewer.getTable( ).select( index + 1);
                    }
                }
                public void widgetDefaultSelected(SelectionEvent e)
                {
                }
                
            });