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
EPartService partService1 = (EPartService) part1.getContext().get(
				EPartService.class.getName());
		assertTrue(partService1.isPartVisible(part1));
		assertFalse(partService1.isPartVisible(part2));
		partService1.activate(part2);
		EPartService partService2 = (EPartService) part2.getContext().get(
				EPartService.class.getName());
		assertFalse(partService1.isPartVisible(part1));
		assertTrue(partService1.isPartVisible(part2));
		assertFalse(partService2.isPartVisible(part1));
		assertTrue(partService2.isPartVisible(part2));
	}
	public void testActivate_partService_twoWindows() {
		MApplication application = createApplication(new String[] {
				"partFrontA", "partBackA" }, new String[] { "partFrontB",
				"partBackB" });
		MWindow windowA = application.getChildren().get(0);
		MPartStack partStackA = (MPartStack) windowA.getChildren().get(0);
		MPart partFrontA = (MPart) partStackA.getChildren().get(0);
		MPart partBackA = (MPart) partStackA.getChildren().get(1);
		partStackA.setSelectedElement(partFrontA);
		windowA.setSelectedElement(partStackA);
		MWindow windowB = application.getChildren().get(1);
		MPartStack partStackB = (MPartStack) windowB.getChildren().get(0);
		MPart partFrontB = (MPart) partStackB.getChildren().get(0);
		MPart partBackB = (MPart) partStackB.getChildren().get(1);
		partStackB.setSelectedElement(partFrontB);
		windowB.setSelectedElement(partStackB);
		application.setSelectedElement(windowA);
		getEngine().createGui(windowA);