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
fActionSet.saveFilterAndSorterState(memento);
	}
	
	private void saveCurrentFrame(IMemento memento) {
        FrameAction action = fActionSet.getUpAction();
        FrameList frameList= action.getFrameList();
		if (frameList.getCurrentIndex() > 0) {
			TreeFrame currentFrame = (TreeFrame) frameList.getCurrentFrame();
			
			if (currentFrame.getInput() instanceof WorkingSetModel)
				return;
			IMemento frameMemento = memento.createChild(TAG_CURRENT_FRAME);
			currentFrame.saveState(frameMemento);
		}
	}
	private void saveLinkingEnabled(IMemento memento) {
		memento.putInteger(PreferenceConstants.LINK_PACKAGES_TO_EDITOR, fLinkingEnabled ? 1 : 0);
	}
	private void saveLayoutState(IMemento memento) {
		if (memento != null) {	
			memento.putInteger(TAG_LAYOUT, getLayoutAsInt());
		} else {
		
			IPreferenceStore store= JavaPlugin.getDefault().getPreferenceStore();
			store.setValue(TAG_LAYOUT, getLayoutAsInt());
		}
	}
	private int getLayoutAsInt() {
		if (fIsCurrentLayoutFlat)
			return FLAT_LAYOUT;