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
assertNotNull(windowService2);
		assertNotNull("The first part is active in the first window",
				windowService1.getActivePart());
		assertNull("There should be nothing active in the second window",
				windowService2.getActivePart());
		
		windowService1.activate(part);
		assertEquals("The part should have been activated", part,
				windowService1.getActivePart());
		assertNull("The second window has no parts, this should be null",
				windowService2.getActivePart());
		
		window2.getChildren().add(part);
		
		windowService2.activate(part);
		assertEquals("No parts in this window, this should be null", null,
				windowService1.getActivePart());
		assertEquals("We activated it just now, this should be active", part,
				windowService2.getActivePart());
	}
	public void testApplicationContextHasActivePart() {
		MApplication application = ApplicationFactoryImpl.eINSTANCE
				.createApplication();
		MWindow window = BasicFactoryImpl.eINSTANCE.createWindow();
		application.getChildren().add(window);
		application.setSelectedElement(window);
		MPart partA = BasicFactoryImpl.eINSTANCE.createPart();
		MPart partB = BasicFactoryImpl.eINSTANCE.createPart();
		window.getChildren().add(partA);
		window.getChildren().add(partB);