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
* 
	 * @see org.eclipse.jface.viewers.StructuredViewer#refresh(java.lang.Object,
	 *      boolean)
	 */
	public void refresh(Object element, boolean updateLabels) {
		
		if(element != getInput()) {
		
			INavigatorPipelineService pipeDream = contentService
					.getPipelineService();
	
			PipelinedViewerUpdate update = new PipelinedViewerUpdate();
			update.getRefreshTargets().add(element);
			update.setUpdateLabels(updateLabels);
			
			if (pipeDream.interceptRefresh(update)) {
				
				boolean toUpdateLabels = update.isUpdateLabels();
				for (Iterator iter = update.getRefreshTargets().iterator(); iter
						.hasNext();) {
					super.refresh(iter.next(), toUpdateLabels);
				}
			} else {
				super.refresh(element, updateLabels);
			}
		} else {
			super.refresh(element, updateLabels);
		}
	}