When I send a mail via SMTP and the blank line between headers and body consists only of an LF instead of CR LF, then James does not recognize it as the separator. Instead, it stores any subsequent body as part of the header blob, I assume as continuation of the last header line.
I also observed this in DSN bounces, where the last part had the rfc822-headers type but included the mail body, when it was sent with an LF-only separator.
I am not sure if this is indeed a bug or just a strict interpretation of the standard. If this is not a bug in your opinion, please feel free to close this ticket.