Sorry, I was using RFC-speak.  A message is divided into 'headers' and 'body', and all of the attachments are part of the body in RFC terms.  But think of it as 'initial headers' and 'everything else'.  Please either attach the full file, and/or try your test using HeaderParser and report the results.

However, it occurs to me that the attachments aren't decoded until you retrieve them, so whatever is going on it must be something other than a decoding issue.  Nevertheless, Parser actually parses the whole message, attachments included, so we'll need the actual message in order to reproduce this (unless you can reproduce it with a smaller message).