Bug 135971 [CommonNavigator] Project Explorer: cannot drop to Hierarchy view
You can drag and drop an element onto the Hierarchy view from the Outline or Package Explorer. You cannot from the Project Explorer, you get a drop disabled cursor.
bundles/org.eclipse.ui.navigator/src/org/eclipse/ui/navigator/CommonViewer.java
control.addMouseListener(new MouseAdapter() {
            public void mouseDown(MouseEvent e) {
            	clearSelectionCache();
            }
        });
    }
	
	/* (non-Javadoc)
	 * @see org.eclipse.jface.viewers.AbstractTreeViewer#setSelectionToWidget(java.util.List, boolean)
	 */
	protected void setSelectionToWidget(List v, boolean reveal) {
		clearSelectionCache();
		super.setSelectionToWidget(v, reveal);
	}
	
	/* (non-Javadoc)
	 * @see org.eclipse.jface.viewers.AbstractTreeViewer#handleDoubleSelect(org.eclipse.swt.events.SelectionEvent)
	 */
	protected void handleDoubleSelect(SelectionEvent event) {
		clearSelectionCache();
		super.handleDoubleSelect(event);
	}
	
	/* (non-Javadoc)
	 * @see org.eclipse.jface.viewers.StructuredViewer#handleOpen(org.eclipse.swt.events.SelectionEvent)
	 */