Bug 327964 EPartService's hidePart may fail when trying to hide a shared part that's in a shared container
The placeholder retrieval code in the EPartService implementation doesn't go far down deep enough and actually stops at the shared container level. This causes the placeholder of the shared part to not be found.
tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/application/EPartServiceTest.java
MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		partA.setElementId("partA");
		partStack.getChildren().add(partA);
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		partB.setElementId("partB");
		partB.setToBeRendered(false);
		partStack.getChildren().add(partB);
		partStack.setSelectedElement(partA);
		window.setSelectedElement(partStack);
		application.setSelectedElement(window);
		initialize(applicationContext, application);
		getEngine().createGui(window);
		EPartService partService = (EPartService) window.getContext().get(
				EPartService.class.getName());
		partService.activate(partA);
		assertEquals(partA, partService.getActivePart());
		MPart shownPart = partService.showPart("partB",
				EPartService.PartState.VISIBLE);
		assertEquals(2, partStack.getChildren().size());
		assertEquals(
				"The part is in the same stack as the active part, so the active part should not have changed",
				partA, partService.getActivePart());
		assertNotNull("The shown part should have a context",
				partB.getContext());
		assertTrue(partService.isPartVisible(partA));
		assertFalse(partService.isPartVisible(partB));
		assertEquals(partB, shownPart);
		assertTrue(partB.isToBeRendered());
	}
	private void testShowPart_Id_Unrendered(EPartService.PartState partState) {