When I deep link to a step of the checkout extensibility checkout, the `event.context.document.title` property is populated. However, when I navigate to a new step, like clicking the "Continue to shipping" button, the new `page_viewed` event that fires has an empty string for the `event.context.document.title`. Other fields, like `event.context.window.location.href` do update on secondary navigation with a valid value.
