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
private void testShowPart_Part_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");
		application.getDescriptors().add(partDescriptor);
		stack.setSelectedElement(part);
		window.setSelectedElement(stack);
		application.setSelectedElement(window);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		MPart createdPart = partService.createPart("partId");
		MPart shownPart = partService.showPart(createdPart, partState);
		assertNotNull(shownPart);
		if (multipleAllowed) {
			assertEquals(createdPart, shownPart);
		} else {
			assertEquals(part, shownPart);
		}
	}
	public void testShowPart_Part_MultipleExists_TrueACTIVATE() {
		testShowPart_Part_MultipleExists(true, PartState.ACTIVATE);
	}
	public void testShowPart_Part_MultipleExists_FalseACTIVATE() {