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
if (items.size() != current.length)
	    		return false;
	    	Set newSelection= new HashSet(items);
	    	for (int i= 0; i < current.length; i++) {
				if (!newSelection.contains(current[i]))
					return false;
			}
	    	return true;
	    }
	    
	    private boolean fInPreserveSelection;
		protected void preservingSelection(Runnable updateCode) {
			try {
				fInPreserveSelection= true;
				super.preservingSelection(updateCode);
			} finally {
				fInPreserveSelection= false;
			}
		}
		protected void setSelectionToWidget(ISelection selection, boolean reveal) {
			if (!fInPreserveSelection || !(selection instanceof MultiElementSelection)) {
				super.setSelectionToWidget(selection, reveal);
				return;
			}
			IContentProvider cp= getContentProvider();
			if (!(cp instanceof IMultiElementTreeContentProvider)) {
				super.setSelectionToWidget(selection, reveal);
				return;
			}
			IMultiElementTreeContentProvider contentProvider= (IMultiElementTreeContentProvider)cp;