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
elements[i]);
						if (!add)
							break;
					}
				}
				if (add)
					filtered.add(elements[i]);
			}
			return filtered.toArray();
		}
		
		/* Checks if a filtered object in essential (ie. is a parent that
		 * should not be removed).
		 */ 
		private boolean isEssential(Object object) {
			try {
				if (!isFlatLayout() && object instanceof IPackageFragment) {
					IPackageFragment fragment = (IPackageFragment) object;
					return !fragment.isDefaultPackage() && fragment.hasSubpackages();
				}
			} catch (JavaModelException e) {
				JavaPlugin.log(e);
			}
			return false;
		}
		
		protected void handleInvalidSelection(ISelection invalidSelection, ISelection newSelection) {
			IStructuredSelection is= (IStructuredSelection)invalidSelection;
			List ns= null;
			if (newSelection instanceof IStructuredSelection) {