Something to try. Figured I'd mess with it more:

When I use the promo site in Firefox (with adblock plus), I get an email with blanks
When I use (YUCK) Internet Explorer, I get an email with the codes.

So try testing that if you are like me and use a different browser.

Also, I entered the Amazon Promo code, and then tried 2 different email addresses. Both email addresses succesfully got codes. The codes were the SAME codes to both emails, so no, you ain't gonna scam the system