Bug 339573 Splitting the shared area with a part doesn't remove stale placeholders
The current code only looks for the addition of an MPlaceholder in the shared area as the hint to remove locals. When you split the area the element that gets added is the new MPartSashContainer...
bundles/org.eclipse.e4.ui.workbench.swt/src/org/eclipse/e4/ui/internal/workbench/swt/PartRenderingEngine.java
return curFactory.getRenderer(uiElement, parent);
	}
	protected AbstractPartRenderer getRendererFor(MUIElement element) {
		return (AbstractPartRenderer) element.getRenderer();
	}
	public Object run(final MApplicationElement uiRoot,
			final IEclipseContext runContext) {
		final Display display;
		if (runContext.get(Display.class) != null) {
			display = runContext.get(Display.class);
		} else {
			display = Display.getDefault();
			runContext.set(Display.class, display);
		}
		Realm.runWithDefault(SWTObservables.getRealm(display), new Runnable() {
			public void run() {
				initializeStyling(display, runContext);
				
				runContext.set(IResourceUtilities.class.getName(),
						new ResourceUtility());
				
				KeyBindingDispatcher dispatcher = (KeyBindingDispatcher) ContextInjectionFactory
						.make(KeyBindingDispatcher.class, runContext);
				runContext.set(KeyBindingDispatcher.class.getName(), dispatcher);
				keyListener = dispatcher.getKeyDownFilter();
				display.addFilter(SWT.KeyDown, keyListener);
				display.addFilter(SWT.Traverse, keyListener);