I'm going to need to see the raw source of the email you're trying to process. It's either a totally empty body, which I can't replicate, or it's some sort of multipart payload which I'm not handling properly.
What email client are you using to send these test messages? Gmail web interface?
Can you view the raw source of one of the emails (in your Sent folder) and post it here?
Thanks!
Edit: Nevermind. I see it is the Gmail web client doing something weird with multipart messages. I'll test more with it and see what I can do.