CiviCRM 4.5.4 on WordPress 4.1 using SMTP and Mandrill as sending framework.
Contribution form URL: https://crm.globalvoicesonline.org/?page_id=41
Contribution form is set to send email receipts: See Attached
Test emails and system emails send perfectly fine.
Email reciepts are marked as sent but are never queued and don't show up in Mandrill log or outbox: See attached
Referred to Web Access for troubleshooting and they indicated a core bug.