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
List treePaths= new ArrayList();
			for (int i= 0; i < selection.length; i++) {
				TreeItem item= selection[i];
				Object element= getElement(item);
				if (element == null)
					continue;
				if (!result.contains(element)) {
					result.add(element);
				}
				treePaths.add(createTreePath(item));
			}
			return new MultiElementSelection(this, result, (TreePath[])treePaths.toArray(new TreePath[treePaths.size()]));
		}
		private TreePath createTreePath(TreeItem item) {
			List result= new ArrayList();
			result.add(item.getData());
			TreeItem parent= item.getParentItem();
			while (parent != null) {
				result.add(parent.getData());
				parent= parent.getParentItem();
			}
			Collections.reverse(result);
			return new TreePath(result.toArray());
		}
		private Object getElement(TreeItem item) {
			Object result= item.getData();
			if (result == null)
				return null;
			return result;
		}