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
*/
	public void removeLocalPlaceholders(MWindow window, MPerspective perspective) {
		List<MPlaceholder> globals = findElements(window, null, MPlaceholder.class, null,
				OUTSIDE_PERSPECTIVE | IN_SHARED_AREA);
		List<MPlaceholder> locals = findElements(perspective, null, MPlaceholder.class, null,
				IN_ANY_PERSPECTIVE);
		for (MPlaceholder local : locals) {
			for (MPlaceholder global : globals) {
				if (global.getRef() == local.getRef()) {
					MElementContainer<MUIElement> localParent = local.getParent();
					local.getParent().getChildren().remove(local);
					setStackVisibility(localParent);
				}
			}
		}
	}
	/**
	 * @param parent
	 */
	private void setStackVisibility(MElementContainer<MUIElement> parent) {
		for (MUIElement child : parent.getChildren()) {
			if (child.isToBeRendered() && child.isVisible()) {
				parent.setToBeRendered(true);
				return;
			}
		}
		parent.setToBeRendered(false);
	}
}