Bug 307747 EPartService doesn't render new parts
1. Have a part in a stack, it is the selected part. 2. Show another part in that stack using PartState.CREATE or PartState.VISIBLE. 3. The part should've been rendered. It is not.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
MPart createdPart = partService.createPart("partId");
		MPart shownPart = partService.showPart(createdPart, PartState.ACTIVATE);
		assertNotNull(shownPart);
		assertEquals(createdPart, shownPart);
		MPart createdPart2 = partService.createPart("partId");
		MPart shownPart2 = partService.showPart(createdPart2,
				PartState.ACTIVATE);
		assertFalse(shownPart.equals(shownPart2));
		assertTrue(stack.getChildren().contains(shownPart));
		assertTrue(stack.getChildren().contains(shownPart2));
	}
	public void testShowPart_Part_ExistingInNonstandardCategory() {
		MApplication application = MApplicationFactory.eINSTANCE
				.createApplication();
		MWindow window = MApplicationFactory.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPartStack stack = MApplicationFactory.eINSTANCE.createPartStack();
		stack.setId("categoryId2");
		window.getChildren().add(stack);
		window.setSelectedElement(stack);
		MPart part = MApplicationFactory.eINSTANCE.createPart();
		part.setId("partId");
		stack.getChildren().add(part);
		stack.setSelectedElement(part);
		MPartDescriptor descriptor = MApplicationFactory.eINSTANCE
				.createPartDescriptor();
		descriptor.setAllowMultiple(true);
		descriptor.setId("partId");
		descriptor.setCategory("categoryId");