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
parentRenderer.hideChild(element.getParent(), element);
		}
		AbstractPartRenderer renderer = getRendererFor(element);
		
		if (renderer != null) {
			if (element instanceof MElementContainer<?>) {
				MElementContainer<MUIElement> container = (MElementContainer<MUIElement>) element;
				MUIElement selectedElement = container.getSelectedElement();
				List<MUIElement> children = container.getChildren();
				for (MUIElement child : children) {
					
					if (child != selectedElement) {
						removeGui(child);
					}
				}
				if (selectedElement != null
						&& children.contains(selectedElement)) {
					
					removeGui(selectedElement);
				}
			}
			if (element instanceof MPerspective) {
				MPerspective perspective = (MPerspective) element;
				for (MWindow subWindow : perspective.getWindows()) {
					removeGui(subWindow);
				}
			} else if (element instanceof MWindow) {
				MWindow window = (MWindow) element;
				for (MWindow subWindow : window.getWindows()) {
					removeGui(subWindow);