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
super.add(parentElement, childElements);
			} else {
				List stable= new ArrayList(l);
				super.add(parentElement, childElements);
				for (Iterator iter= stable.iterator(); iter.hasNext();) {
					Widget item= (Widget)iter.next();
					super.internalAdd(item, parentElement, childElements);				
				}
			}
		}
				
		protected Object[] getRawChildren(Object parent) {
			try {
				fPendingGetChildren.add(parent);
				return super.getRawChildren(parent);				
			} finally {
				fPendingGetChildren.remove(parent);
			}
		}
		
		/*
		 * @see org.eclipse.jface.viewers.StructuredViewer#filter(java.lang.Object)
		 */
		protected Object[] getFilteredChildren(Object parent) {
			List list = new ArrayList();
			ViewerFilter[] filters = fViewer.getFilters();
			Object[] children = ((ITreeContentProvider) fViewer.getContentProvider()).getChildren(parent);
			for (int i = 0; i < children.length; i++) {
				Object object = children[i];
				if (!isEssential(object)) {