Checking to see if this is happening to anyone else. This is a clever tactic where spammers are exploiting the GMail mail delivery subsystem with a return path to a legit GMail address to have the subsystem deliver the original spam message as an attachment to the recipient.
It's been happening to me too. I don't want to flag the messages as spam, as the mail delivery subsystem is doing exactly as it is supposed to, but this is a problem.