Ensure $entity->metatags can be saved programmatically from a loaded entity only

Just some more info related to this, in metatag_metatags_save():

  // Certain modules, e.g. Workbench Moderation, will cause the data to be in
  // an unsupported format; the problem needs to be resolved elsewhere so this
  // can only be considered a temporary fix.
  // TODO: Solve the core problem, which will probably entail something
  // similar to http://drupal.org/node/1876034.
  if (isset($metatags[$language])) {

But the issue wasn't with Workbench moderation. It was metatag that cannot save its own loaded data. If you do node_save(node_load($nid)); your metatags are broken with the current beta version. The beta version assumed your node was saved after a submit. The isset check solves this.

The issue isn't we need to match core strucutre, because it isn't a field at all. The issue is just that we need to be consistent.

Ok, that comment is more fair. :)