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
public void testShowPart_Part_ExistingInNonstandardCategory() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPartStack stack = BasicFactoryImpl.eINSTANCE.createPartStack();
		stack.setElementId("categoryId2");
		window.getChildren().add(stack);
		window.setSelectedElement(stack);
		MPart part = BasicFactoryImpl.eINSTANCE.createPart();
		part.setElementId("partId");
		stack.getChildren().add(part);
		stack.setSelectedElement(part);
		MPartDescriptor descriptor = org.eclipse.e4.ui.model.application.descriptor.basic.impl.BasicFactoryImpl.eINSTANCE
				.createPartDescriptor();
		descriptor.setAllowMultiple(true);
		descriptor.setElementId("partId");
		descriptor.setCategory("categoryId");
		application.getDescriptors().add(descriptor);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart shownPart = partService.showPart("partId", PartState.ACTIVATE);
		assertEquals(part, shownPart);
		assertEquals(stack, part.getParent());
	}
	public void testShowPart_Bug318931() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE