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 activate(MPart part, boolean requiresFocus) {
		activate(part, requiresFocus, true);
	}
	private void activate(MPart part, boolean requiresFocus, boolean activateBranch) {
		
		if (!isInContainer(part)) {
			return;
		}
		MWindow window = getWindow();
		IEclipseContext windowContext = window.getContext();
		
		if (windowContext.getParent().getActiveChild() == windowContext && part == activePart) {
			return;
		}
		modelService.bringToTop(part);
		window.getParent().setSelectedElement(window);
		partActivationHistory.activate(part, activateBranch);
		Object object = part.getObject();
		if (object != null && requiresFocus) {
			ContextInjectionFactory.invoke(object, Focus.class, part.getContext(), null);
		}
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see org.eclipse.e4.ui.workbench.modeling.EPartService#getActivePart()
	 */
	public MPart getActivePart() {
		return activePart;
	}