Thanks for posting.
I was able to reproduce this issue with FileMaker Pro 11v2 and FileMaker Pro 11v3 sending through Entourage 2008. It appears that the message is created but it's put in the drafts folder and not presented to the user.
I did not get this behavior when I tried with Outlook 2011 and I was also unable to reproduce this issue with any mail client on Windows. I've forwarded your post and my findings to our Development and Quality Assurance (testing) departments for further review and confirmation.