Bug 319169 [UI] active parts in Detached windows prevent activating a part in the main window
Start with a fresh WS Detach the Outline view using DnD Now you can no longer activate any part in the main window (i.e. Package Explorer). The cause seems to be that the 'rootContainer' has become the DW's MTrimmedWindow rather than the DW's containing MPerspective. This causes the PartService's 'activate' to fail the 'isInContainer()' test...
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/HeadlessContextPresentationEngine.java
private boolean createContributions = true;
	protected IEclipseContext getParentContext(MUIElement element) {
		MElementContainer<MUIElement> parent = element.getParent();
		IEclipseContext context = null;
		while (parent != null) {
			if (parent instanceof MContext) {
				return ((MContext) parent).getContext();
			}
			parent = parent.getParent();
		}
		return context;
	}
	private static void populateModelInterfaces(MContext contextModel,
			IEclipseContext context, Class<?>[] interfaces) {
		for (Class<?> intf : interfaces) {
			Activator.trace(Policy.DEBUG_CONTEXTS,
					"Adding " + intf.getName() + " for " 
							+ contextModel.getClass().getName(), null);
			context.set(intf.getName(), contextModel);
			populateModelInterfaces(contextModel, context, intf.getInterfaces());
		}
	}
	@PostConstruct
	void postConstruct() {
		childHandler = new EventHandler() {
			public void handleEvent(Event event) {
				if (UIEvents.EventTypes.ADD.equals(event
						.getProperty(UIEvents.EventTags.TYPE))) {
					Object element = event
							.getProperty(UIEvents.EventTags.NEW_VALUE);