Missing bundle for entity type taxonomy_term

I think it's a bug - this can't be a feature. Error while creating taxonomy terms via php-script. It seems, not to be allowed to use a private variable for setting the "vid" in the "taxonomy_term". If a public variable or method is used everything fine, but local variables always failed.

	$vocabularyMachineName = 'example_vocabulary';	
	$vocNode = array(
					'name' => 'Example Vokabulary',
					'vid' => $vocabularyMachineName,
					'description' => 'Descripe this vocabulary',
				); 
	\Drupal::entityManager()->getStorage('taxonomy_vocabulary')->create($vocNode)->save();

	
	$termNode = array(	
					'vid' =>$vocabularyMachineName, 	
					'name' => 'Example Taxonomy',
					'description' =>  'Describe this Taxonomy',
				);
	\Drupal::entityManager()->getStorage('taxonomy_term')->create($termNode)->save();