Bug 127105 Package explorer hierarchical mode calls ICompilationUnit#getChildren() in PackageExplorerProblemTreeViewer#isExpandable
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
if (fMemento != null) {
			restoreLinkingEnabled(fMemento);
		}
		
		makeActions(); 
		
		
		restoreFilterAndSorter();
		fViewer.setInput(findInputElement());
		initFrameActions();
		initKeyListener();
			
		fViewer.addPostSelectionChangedListener(fPostSelectionListener);
		
		fViewer.addDoubleClickListener(new IDoubleClickListener() {
			public void doubleClick(DoubleClickEvent event) {
				fActionSet.handleDoubleClick(event);
			}
		});
		
		fViewer.addOpenListener(new IOpenListener() {
			public void open(OpenEvent event) {
				fActionSet.handleOpen(event);
				fLastOpenSelection= event.getSelection();
			}
		});
		IStatusLineManager slManager= getViewSite().getActionBars().getStatusLineManager();
		fViewer.addSelectionChangedListener(new StatusBarUpdater(slManager));
		fViewer.addTreeListener(fExpansionListener);