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
return false;
		if (tagsToMatch != null) {
			List<String> elementTags = element.getTags();
			for (String tag : tagsToMatch) {
				if (!elementTags.contains(tag))
					return false;
			}
		}
		return true;
	}
	private <T> void findElementsRecursive(MUIElement searchRoot, String id,
			Class<? extends T> type, List<String> tagsToMatch, List<T> elements) {
		
		if (match(searchRoot, id, type, tagsToMatch)) {
			if (!elements.contains((T) searchRoot))
				elements.add((T) searchRoot);
		}
		
		if (searchRoot instanceof MElementContainer<?>) {
			MElementContainer<MUIElement> container = (MElementContainer<MUIElement>) searchRoot;
			List<MUIElement> children = container.getChildren();
			for (MUIElement child : children) {
				findElementsRecursive(child, id, type, tagsToMatch, elements);
			}
		}
		
		if (searchRoot instanceof MTrimmedWindow) {
			MTrimmedWindow tw = (MTrimmedWindow) searchRoot;
			List<MTrimBar> bars = tw.getTrimBars();
			for (MTrimBar bar : bars) {