Bug 329482 Uninstantiated part may be rendered when closing another part in the same stack
1. Activate the 'Javadoc' view. 2. Activate the 'Package Explorer' view. 3. Shutdown. 4. Restart. 5. Ctrl+3 > Properties 6. Hide the 'Properties' view. 7. Now the 'Problems' view is the selected element. It should be the 'Javadoc' view.
bundles/org.eclipse.e4.ui.workbench/src/org/eclipse/e4/ui/internal/workbench/PartActivationHistory.java
if (parent == null && element instanceof MWindow) {
			
			parent = (MUIElement) ((EObject) element).eContainer();
		}
		if (parent == null) {
			return isValid(partService.getLocalPlaceholder(element));
		}
		return isValid(parent);
	}
	/**
	 * Checks to see if this element and its parents are actually being rendered.
	 */
	boolean isValid(MPerspective perspective, MUIElement element) {
		if (element instanceof MApplication) {
			return true;
		} else if (element == null || !element.isToBeRendered() || !element.isVisible()) {
			return false;
		}
		MElementContainer<?> parent = element.getParent();
		if (parent == null) {
			for (MPlaceholder placeholder : modelService.findElements(perspective, null,
					MPlaceholder.class, null)) {
				if (placeholder.getRef() == element) {
					return isValid(perspective, placeholder);
				}
			}
			if (element instanceof MWindow) {
				
				return isValid(perspective, (MUIElement) ((EObject) element).eContainer());
			}