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/internal/workbench/ModelServiceImpl.java
/**
	 * Determine if the element passes the matching test for all non-null parameters.
	 * 
	 * @param element
	 *            The element to test
	 * @param id
	 *            The Id
	 * @param clazz
	 *            The class that element must be an instance of
	 * @param tagsToMatch
	 *            The tags to check, <b>all</b> the specified rags must be in the element's tags
	 * @return <code>true</code> iff all the tests pass
	 */
	private boolean match(MUIElement element, String id, Class clazz, List<String> tagsToMatch) {
		if (id != null && !id.equals(element.getElementId()))
			return false;
		if (clazz != null && !(clazz.isInstance(element)))