This issue could be related to the new Magento Email Queue system, that leaves orphan records on the Recipients table.

If this is your issue, I've sent a fix on this post: http://magento.stackexchange.com/a/87299/23057

This issue could be related to the new Magento Email Queue system, that leaves orphan records on the Recipients table.

If this is your issue, I've sent a fix on this post: https://magento.stackexchange.com/a/87299/23057