Bug 329184 Detached view that is an activation target candidate can prevent perspective switching
1. Detach the 'Outline' view. 2. Window > Open Perspective > Debug 3. Window > Open Perspective > Java 4. The perspective switch doesn't actually happen. You see the 'Debug' perspective's content with an 'Outline' view detached. Closing the 'Outline' view in the 'Debug' perspective will workaround this problem.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
stack.getChildren().add(placeholderA);
		stack.setSelectedElement(placeholderA);
		MPlaceholder placeholderB = AdvancedFactoryImpl.eINSTANCE
				.createPlaceholder();
		partB.setCurSharedRef(placeholderB);
		placeholderB.setRef(partB);
		stack.getChildren().add(placeholderB);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partA);
		partService.activate(partB);
		partService.activate(partA);
		partService.hidePart(partA);
		assertEquals(placeholderB, stack.getSelectedElement());
		assertEquals(partB, partService.getActivePart());
		partService.hidePart(partB);
		assertNull(stack.getSelectedElement());
		assertNull(partService.getActivePart());
	}
	public void testHidePart_ActivationHistory07() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		window.getSharedElements().add(partA);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		window.getSharedElements().add(partB);