Bug 323832 [UI] SashContainers are not being removed when unneeded
Start with a fresh workspace Drag the Problems view to the right of its current stack Drag it back... The problem is that the original drag created an MPartSashContainer to host the new stack but the drag back doesn't remove it (i.e. after dragging the Problems view back to its original stack there's now an MPSC with *only* the one stack in it).
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/workbench/modeling/EModelService.java
*            The element to move
	 * @param newParent
	 *            The new parent for the element.
	 * @param index
	 *            The index to insert the element at; -1 means at the end
	 */
	public void move(MUIElement element, MElementContainer<MUIElement> newParent, int index);
	/**
	 * Move the element to a new location. The element will be placed at the end of the new parent's
	 * list of children.
	 * 
	 * @param element
	 *            The element to move
	 * @param newParent
	 *            The new parent for the element.
	 * @param index
	 *            The index to insert the element at; -1 means at the end
	 * @param leavePlaceholder
	 *            true if a placeholder for the element should be added
	 */
	public void move(MUIElement element, MElementContainer<MUIElement> newParent, int index,
			boolean leavePlaceholder);
	/**
	 * Inserts the given element into the UI Model by either creating a new sash or augmenting an
	 * existing sash if the orientation permits.
	 * 
	 * @param toInsert
	 *            The element to insert
	 * @param relTo
	 *            The element that the new one is to be relative to