Bug 326177 EPartService's getActivePart() does not appear to work properly for an application with multiple windows
Based on the code in PartServiceCreationFunction, the EPartService implementation being returned when an application's context is queried seems to be a window-level EPartService implementation.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
public void testActivate_Focus() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		partA.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.application.ClientEditor");
		window.getChildren().add(partA);
		window.setSelectedElement(partA);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partB.setContributionURI("platform:/plugin/org.eclipse.e4.ui.tests/org.eclipse.e4.ui.tests.application.ClientEditor");
		window.getChildren().add(partB);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		ClientEditor editorB = (ClientEditor) partB.getObject();
		assertFalse(editorB.wasFocusCalled());
		EPartService partService = window.getContext().get(EPartService.class);
		partService.activate(partB);
		assertTrue(editorB.wasFocusCalled());
	}
	public void testActivate_ChildWindow() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		window.getChildren().add(partA);
		window.setSelectedElement(partA);
		MWindow detachedWindow = BasicFactoryImpl.eINSTANCE.createWindow();