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/EPartServiceTest.java
MApplication application = createApplication(1, new String[1][0]);
		MWindow window = application.getChildren().get(0);
		MPartDescriptor partDescriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		partDescriptor.setElementId("partId");
		application.getDescriptors().add(partDescriptor);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		assertNull(partService.showPart("partId2", partState));
	}
	public void testShowPart_Id_IncorrectDescriptor_ACTIVATE() {
		testShowPart_Id_IncorrectDescriptor(PartState.ACTIVATE);
	}
	public void testShowPart_Id_IncorrectDescriptor_VISIBLE() {
		testShowPart_Id_IncorrectDescriptor(PartState.VISIBLE);
	}
	public void testShowPart_Id_IncorrectDescriptor_CREATE() {
		testShowPart_Id_IncorrectDescriptor(PartState.CREATE);
	}
	private void testShowPart_Id_MultipleExists(boolean multipleAllowed,
			PartState partState) {
		MApplication application = createApplication("partId");
		MWindow window = application.getChildren().get(0);
		MPartStack stack = (MPartStack) window.getChildren().get(0);
		MPart part = (MPart) stack.getChildren().get(0);
		MPartDescriptor partDescriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		partDescriptor.setAllowMultiple(multipleAllowed);
		partDescriptor.setElementId("partId");