[Mailman-Users] Message footers as "inline attachment"

[Web Witchcraft]

A few months back our mailman listserv started showing up with an occasional
short message sent out to the list members who receive individual messages
that had the usual message footers attached as an "inline attachment" rather
than including it in the body of the message. It went on this way for months
with only an occasional rare message showing the footers as an inline
attachment but it gradually got worse until NOW someone complained about it
and when I started looking I realized that 9 out of 10 of our messages now
show the footers as an attachment to the message email rather than being in
the body of the email. 

The odd thing is that it happens for MOST users but some members seem to be
immune to the issue. A scan through my two message private archives for this
list shows that some list members don't seem to EVER have the problem while
MOST list members do...

I'm completely baffled here. For the LIFE of me I can't figure out what
would cause this to happen. Yet it clearly IS happening. 

Can anyone here offer a suggestion as to what the cause of this strange
behavior may be and how to correct it?

Thanks!