Bug 64890 Package explorer out of sync when open/closing projects [package explorer]
RC1 - close a project - Open the closed project in a new window va Open in New Window context menu action - open the project observe: the Java project is rendered in the additional window as folders and CUs not on the class path.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/packageview/PackageExplorerActionGroup.java
private void addOpenNewWindowAction(IMenuManager menu, Object element) {
		if (element instanceof IJavaElement) {
			element= ((IJavaElement)element).getResource();
			
		}
		if (!(element instanceof IContainer))
			return;
		menu.appendToGroup(
			IContextMenuConstants.GROUP_OPEN, 
			new OpenInNewWindowAction(fPart.getSite().getWorkbenchWindow(), (IContainer)element));
	}
	
	 void handleDoubleClick(DoubleClickEvent event) {
		TreeViewer viewer= fPart.getViewer();
		Object element= ((IStructuredSelection)event.getSelection()).getFirstElement();
		if (viewer.isExpandable(element)) {
			if (doubleClickGoesInto()) {
				
				if (element instanceof ICompilationUnit || element instanceof IClassFile)
					return;
				if (element instanceof IOpenable || element instanceof IContainer) {
					fZoomInAction.run();
				}
			} else {
				IAction openAction= fNavigateActionGroup.getOpenAction();
				if (openAction != null && openAction.isEnabled() && OpenStrategy.getOpenMethod() == OpenStrategy.DOUBLE_CLICK)
					return;
				viewer.setExpandedState(element, !viewer.getExpandedState(element));
			}
		}