mm-inline-media-tests change causes more changes than expected

[Dale Hagglund <rdh@best.com>]

I'm running gnu emacs 20.3 with pgnus 0.98.  I added the following
lines to my .gnus file:

      (setq mm-inline-media-tests 
        (cons '("text/html" nil (lambda (h) nil)) mm-inline-media-tests))

The goal here was to prevent gnus from attempting to inline html parts
using w3.  This was failing trying to find x-mouse.el, which probably
means that I have an old version of w3.

I could, of course, have upgraded to a newer version of w3, but my
actual goal was to view the occasional bit of html-only mail with
lynx, and avoid w3 entirely.  Somewhat heretical, I realize, but there
you have it.

After modifying mm-inline-media-tests as shown above, text/html
messages show up with a button, and the raw html shown inline.
Hitting return on the button twice runs lynx, as specified in my
.mailcap file.

However, now, whenever I get multipart/mixed messages, any text/plain
parts are presented with buttons as well.  Messages bodies marked as
text/plain in the headers, either explicitly or implicitly, display
normally.

So, my questions are:

1) Is changing mm-inline-media-tests as above the correct way to
   achieve my goal?

2) Why does the modification affect the display of text/plain parts?

3) What do I need to do to prevent gnus from using w3 to inline
   text/html parts, without disturbing the display of other text/*
   parts.

4) With the above change, text/html parts are displayed with buttons
   in the article buffer, and the raw html displayed inline.  This
   means that I have to click (or the equivalent) on the button twice
   to start lynx.  How can I tell gnus to display text/html parts as
   initially hidden.

Dale.