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
MPerspective perspective = AdvancedFactoryImpl.eINSTANCE
				.createPerspective();
		perspectiveStack.getChildren().add(perspective);
		perspectiveStack.setSelectedElement(perspective);
		MPartStack partStackA = BasicFactoryImpl.eINSTANCE.createPartStack();
		perspective.getChildren().add(partStackA);
		perspective.setSelectedElement(partStackA);
		MPlaceholder placeholderA = AdvancedFactoryImpl.eINSTANCE
				.createPlaceholder();
		partStackA.getChildren().add(placeholderA);
		partStackA.setSelectedElement(placeholderA);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		window.getSharedElements().add(partA);
		partA.setCurSharedRef(placeholderA);
		placeholderA.setRef(partA);
		MPartStack partStackB = BasicFactoryImpl.eINSTANCE.createPartStack();
		perspective.getChildren().add(partStackB);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = window.getContext().get(EPartService.class);
		MPlaceholder placeholderB = partService
				.createSharedPart("partId", true);
		MPart partB = (MPart) placeholderB.getRef();
		partB.setCurSharedRef(placeholderB);
		placeholderB.setToBeRendered(false);
		partB.setToBeRendered(false);
		partStackB.getChildren().add(placeholderB);
		partStackB.setSelectedElement(null);
		partService.showPart(partB, PartState.VISIBLE);
		assertNotNull(partStackB.getSelectedElement());