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/src/org/eclipse/e4/ui/internal/workbench/ModelServiceImpl.java
return null;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.eclipse.e4.ui.workbench.modeling.EModelService#getTrim(org.eclipse.e4.ui.model.application
	 * .ui.basic.MTrimmedWindow, org.eclipse.e4.ui.model.application.ui.SideValue)
	 */
	public MTrimBar getTrim(MTrimmedWindow window, SideValue sv) {
		List<MTrimBar> bars = window.getTrimBars();
		for (MTrimBar bar : bars) {
			if (bar.getSide() == sv)
				return bar;
		}
		
		MTrimBar newBar = BasicFactoryImpl.eINSTANCE.createTrimBar();
		newBar.setSide(sv);
		window.getTrimBars().add(newBar);
		return newBar;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.eclipse.e4.ui.workbench.modeling.EModelService#getTopLevelWindowFor(org.eclipse.e4.ui
	 * .model .application.ui.MUIElement)
	 */
	public MWindow getTopLevelWindowFor(MUIElement element) {
		EObject eObj = (EObject) element;