multipart/related mime type

I'm having some trouble dealing with multipart/related messages.

I set up the rc file with the following argument
<mimefilters>
...
..
multipart/related:m2h_text_plain'filter:mhtxtplain.pl
..

The messages are handled by MHonArc but the body of
the message is appearing twice.

Any hints ?

Thanks
--
Bernard Frit