Drush cc all clears custom fields from Drupal Views

Create a Drupal View using custom data from CiviCRM contacts.
Save
run drush cc all on the command line
Reload the admin page for the View
Observe that the custom fields have gone missing, and are not available in the field list.

Load the page for the view while logged out. Observe that all custom fields are still missing.
Click save on the View.
Observe that the custom fields are now present in the list.

(CRM-21091 also relates to `drush cc all` not doing the expected thing, in that case because of Drush not operating as an authenticated, permissioned user.)