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
engine.applyStyles((Widget) widget, true);
				}
				public CSSStyleDeclaration getStyle(Object widget) {
					return engine.getStyle((Widget) widget);
				}
				public void setClassnameAndId(Object widget, String classname,
						String id) {
					((Widget) widget).setData(
							"org.eclipse.e4.ui.css.CssClassName", classname); 
					((Widget) widget).setData("org.eclipse.e4.ui.css.id", id); 
					engine.applyStyles((Widget) widget, true);
				}
			});
		} else if (cssURI != null) {
			String cssResourcesURI = (String) appContext
					.get(E4Workbench.CSS_RESOURCE_URI_ARG);
			final CSSSWTEngineImpl engine = new CSSSWTEngineImpl(display, true);
			if (cssResourcesURI != null) {
				engine.getResourcesLocatorManager().registerResourceLocator(
						new OSGiResourceLocator(cssResourcesURI.toString()));
			}
			display.setData("org.eclipse.e4.ui.css.context", appContext); 
			appContext.set(IStylingEngine.SERVICE_NAME, new IStylingEngine() {
				public void setClassname(Object widget, String classname) {
					((Widget) widget).setData(
							"org.eclipse.e4.ui.css.CssClassName", classname); 
					engine.applyStyles((Widget) widget, true);
				}
				public void setId(Object widget, String id) {
					((Widget) widget).setData("org.eclipse.e4.ui.css.id", id);