In Drupal 8.0.0, an entity's local ID (e.g., nid for nodes) and revision ID (e.g., vid for nodes) were excluded from normalization/serialization to the HAL format, e.g. for the response to a GET of an entity resource.
In Drupal 8.1.0, these fields are now included to support use cases where they're needed (e.g., constructing a URL to a View that requires these for contextual filters).
Code that uses the HAL format to deploy content from one site to another or across environments (e.g., dev/stage/prod) of a site may need to be adjusted to take this into account. For example, because a POST request to create the entity on the target site MUST NOT include a local ID, it is now the responsibility of content deployment code to strip it after retrieving the GET resource from the source site, rather than implicitly relying on it not being there.
