Bug 81426 Package Explorer shows nothing after drill into working set, then show projects
I200412160800 - switch Package Explorer to working sets - context menu > Go Into a working set - Show > Projects -> view is empty -> view toolbar button 'Up to Working Sets' does not do anything
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerPart.java
}
			} else {
				l.remove(item);
				fResourceToItemsMapper.removeFromMap(element, (Item) item);
			}
			if (l.size() == 0)
				fAdditionalMappings.remove(element);
		}
		protected void unmapAllElements() {
			fAdditionalMappings.clear();
			super.unmapAllElements();
		}
		public void remove(Object[] elements) {
			super.remove(elements);
			List stillExisting= new ArrayList();
			do {
				stillExisting.clear();
				for (int i= 0; i < elements.length; i++) {
					if (findItem(elements[i]) != null)
						stillExisting.add(elements[i]);
				}
				if (stillExisting.size() > 0)
					super.remove(stillExisting.toArray());
			} while (stillExisting.size() > 0);
		}
		protected void internalRefresh(Object element, boolean updateLabels) {
			List l= (List)fAdditionalMappings.get(element);
			if (l == null) {
				super.internalRefresh(element, updateLabels);
			} else {