Bug 81877 Package explorer forgets active working set [package explorer]
3.1 M4 1. open pkg explorer. 2. select a working set, pkg explorer updates and filters out projects. 3. close pkg explorer. 4. open package explorer again and the working set is no longer applied. This used to work.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
ns= new ArrayList(((IStructuredSelection)newSelection).toList());
			} else {
				ns= new ArrayList();
			}
			boolean changed= false;
			for (Iterator iter= is.iterator(); iter.hasNext();) {
				Object element= iter.next();
				if (element instanceof IJavaProject) {
					IProject project= ((IJavaProject)element).getProject();
					if (!project.isOpen()) {
						ns.add(project);
						changed= true;
					}
				} else if (element instanceof IProject) {
					IProject project= (IProject)element;
					if (project.isOpen()) {
						IJavaProject jProject= JavaCore.create(project);
						if (jProject != null && jProject.exists())
							ns.add(jProject);
							changed= true;
					}
				}
			}
			if (changed) {
				newSelection= new StructuredSelection(ns);
				setSelection(newSelection);
			}
			super.handleInvalidSelection(invalidSelection, newSelection);
		}