Download Mail - blank messages

I've just installed the Download Mail plugin and configured it with a POP3 account.

It's all working as expected and has downloaded message, but the only information in the 'Incoming Mail' section is the email header. There's no content to the HTML or text part of the email. I've set testmode to true so the email stays on the server and can see that the email does have content.

Is there a way I can debug this?

Thanks, Paul.