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
MPart shouldBeCorrect = (MPart) partFrontA.getContext().get(
				IServiceConstants.ACTIVE_PART);
		assertNotNull(shouldBeCorrect);
		assertEquals(partBackA, partServiceA.getActivePart());
		partServiceB.activate(partBackB);
		assertEquals(windowB, application.getSelectedElement());
		shouldBeCorrect = (MPart) partFrontB.getContext().get(
				IServiceConstants.ACTIVE_PART);
		assertNotNull(shouldBeCorrect);
		assertEquals(partBackB, partServiceB.getActivePart());
	}
	public void testActivate_Unrendered() {
		MApplication application = createApplication("partFront", "partBack");
		MWindow window = application.getChildren().get(0);
		MPartStack partStack = (MPartStack) window.getChildren().get(0);
		MPart partFront = (MPart) partStack.getChildren().get(0);
		MPart partBack = (MPart) partStack.getChildren().get(1);
		partBack.setToBeRendered(false);
		partStack.setSelectedElement(partFront);
		window.setSelectedElement(partStack);
		application.setSelectedElement(window);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		assertFalse(partBack.isToBeRendered());
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		partService.activate(partBack);
		assertTrue("Activating a part should cause it to be rendered",
				partBack.isToBeRendered());
	}