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.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartServiceImpl.java
public void deactivate(MPart part) {
		logger.warn("EPartService's deactivate(MPart) method will be removed in 1.1M4.",  
				new Throwable());
		MElementContainer<MUIElement> parent = part.getParent();
		MPart oldSelectedElement = (MPart) parent.getSelectedElement();
		if (oldSelectedElement == part) {
			parent.setSelectedElement(null);
			internalFixContext(null, oldSelectedElement);
		}
	}
	private MPartDescriptor findDescriptor(String id) {
		for (MPartDescriptor descriptor : application.getDescriptors()) {
			if (descriptor.getElementId().equals(id)) {
				return descriptor;
			}
		}
		return null;
	}
	private MPart createPart(MPartDescriptor descriptor) {
		if (descriptor == null) {
			return null;
		}
		MPart part = BasicFactoryImpl.eINSTANCE.createPart();
		part.setElementId(descriptor.getElementId());
		part.getMenus().addAll(EcoreUtil.copyAll(descriptor.getMenus()));
		if (descriptor.getToolbar() != null) {
			part.setToolbar((MToolBar) EcoreUtil.copy((EObject) descriptor.getToolbar()));
		}
		part.setCloseable(descriptor.isCloseable());
		part.setContributionURI(descriptor.getContributionURI());