Bug 32664 Package Explorer: hierarchical layout and back-linking don't work allways together.
The following triggers it: - initially 'flat layout' is used, 'link with editor' is on or off - open a java file - use 'collapse all' in the package explorer - select 'hierarchical layout' - switch 'link with editor' on or off&on -> no back-linking
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerContentProvider.java
if (parentElement instanceof IProject) 
				return ((IProject)parentElement).members();
					
			if (needsToDelegate(parentElement)) {
				Object[] packageFragments= fPackageFragmentProvider.getChildren(parentElement);
				children= getWithParentsResources(packageFragments, parentElement);
			} else {
				children= super.getChildren(parentElement);
			}
	
			if (parentElement instanceof IJavaProject) {
				IJavaProject project= (IJavaProject)parentElement;
				return rootsAndContainers(project, children);
			}
			else
				return children;
		} catch (CoreException e) {
			return NO_CHILDREN;
		}
	}
	private Object[] rootsAndContainers(IJavaProject project, Object[] roots) { 
		List result= new ArrayList(roots.length);
		Set containers= new HashSet(roots.length);
		for (int i= 0; i < roots.length; i++) {
			if (roots[i] instanceof IPackageFragmentRoot) {
				IPackageFragmentRoot root= (IPackageFragmentRoot)roots[i];
				IClasspathEntry entry= null;
				try {
					entry= root.getRawClasspathEntry();
				} catch (JavaModelException e) {