Undefined variables: entity_type & entity in Entity->label() in Entity class

I am learning how to work with this new entity functionality using the 7.x-1.x-dev of Entity API, so pardon me if this is a foolish issue.

I defined my entity according to the guidelines, specifically 'label callback' with my own function in hook_entity_info() and wrote that label function properly. When I went to test it, via my_entity->label(), I received these errors:

Notice: Undefined variable: entity_type in Entity->label() (line 101 of .../sites/all/modules/entity/includes/entity.inc).
Notice: Undefined variable: entity in Entity->label() (line 101 of .../sites/all/modules/entity/includes/entity.inc).

After a long while of scrutinizing my own code, I checked out the line in entity.inc and there it has:

public function label() {
  if (isset($this->entityInfo['label callback']) && $this->entityInfo['label callback'] == 'entity_class_label') {
    return $this->defaultLabel();
  }
  return entity_label($entity_type, $entity); //<--------------- ERROR POINTS HERE
}

$entity_type and $entity are not defined in the function and look as if it was copied & pasted from the API page. So, by OOP theory, I changed the line to:

  return entity_label($this->entityType, $this);

just like the uri function just below it and it worked perfectly.

-Marcus