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 MPlaceholder findPlaceholderFor(MWindow window, MUIElement element) {
		List<MPlaceholder> phList = findPerspectiveElements(window, null, MPlaceholder.class, null);
		for (MPlaceholder ph : phList) {
			if (ph.getRef() == element)
				return ph;
		}
		return null;
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.eclipse.e4.ui.workbench.modeling.EModelService#move(org.eclipse.e4.ui.model.application.
	 * MUIElement, org.eclipse.e4.ui.model.application.MElementContainer)
	 */
	public void move(MUIElement element, MElementContainer<MUIElement> newParent) {
		move(element, newParent, -1, false);
	}
	/*
	 * (non-Javadoc)
	 * 
	 * @see
	 * org.eclipse.e4.ui.workbench.modeling.EModelService#move(org.eclipse.e4.ui.model.application.
	 * MUIElement, org.eclipse.e4.ui.model.application.MElementContainer, boolean)
	 */
	public void move(MUIElement element, MElementContainer<MUIElement> newParent,
			boolean leavePlaceholder) {
		move(element, newParent, -1, leavePlaceholder);
	}