Do not specify bundle keys in hook_entity_info() if the entity does not have bundles. This can lead to unexpected behavior with entityreference fields where suddenly the selectbox for mailchimp lists is empty.
I confirm that the above patch works for me. Additionally, the 'type' field doesn't exist in the MailChimp list schema, so this needs to go.
Automatically closed -- issue fixed for 2 weeks with no activity.
Drupal is a registered trademark of Dries Buytaert.