Drupal 7 page cache does not respect the Vary header

Issue

Drupal 7 Page Cache does not currently support variations in cache using the Vary header.

Affected Applications/Limitations

Any Drupal 7 application with page cache enabled attempting to use the Vary header for variations in cache.

Resolution

As a current workaround you can disable page cache by adding the following snippet in settings.php:

$conf['cache_class_cache_page'] = 'DrupalFakeCache';