Gnus not rendering html anymore

[cothrige]

I have been using Gnus 5.11 for a little while now, and loving it.
Somehow I had managed to get w3m working okay with it, and it was
automatically rendering any email which was unfortunately html just
fine.  However, I have noticed that recently, for reasons unknown to me,
html mail no longer renders automatically.  I have looked at the manuals
and gone through the options I can find related to mime, html, w3m and
gnus and everything seems okay.  I don't have text/html, or anything at
all actually, listed in the discouraged list.  But, still, nothing. 

I did try setting the gnus-treat-wash-html variable to 't' myself, and
this worked, but it rendered any non-html mail unreadable.  Obviously,
that won't do.  I currently have to type W-h, which is not a killer, but
I didn't have to do it a few weeks ago, and now I do, and would rather
figure out what I have messed up.  I noticed also in the docs that W-h
"is usually done automatically by Gnus if the message in question has a
`Content-Type' header that says that the message is HTML."  The last
message I have gotten like this definitely had this header and so I
would think should have been handled properly.

What might I be able to do to get html handled properly without my
intervention, and without messing up all the text messages?