🚀 go-pugleaf

I'm using VM 8.2.0b, and recently switched from Emacs 21.4 on RHEL5 to
Emacs 23.1 on RHEL6.

I'm used to having HTML shown inline using the default mechanism using
w3 or whatever it is called.  And that still works SOME OF THE TIME.
But occasionally, when I move to an HTML mail, instead Firefox is
started showing my mail.

I get error messages in *Messages* which I believe, without knowing
for sure, to be related:

    Inlining text/html by emacs-w3m...
    Decoding quoted-printable... done
    Inline text/html by emacs-w3m display failed: Args out of range: 1, 1
    Decoding quoted-printable... done
    Wrote /tmp/vm24421537327.html
    Decoding MIME message... done

That "args out of range" looks suspicious, but I'm not sure what to
make out of it.

This is not specific to particular messages.  The very same message
can be shown correctly one time, and the next time I move to it, it
triggers Firefox.

I might have done something wrong in my configurations, but I don't
know what it might be.  I have not been able to reproduce it with
emtpy configurations, but since it only happens occasionally, I'm not
sure if that means anything.

Any ideas on how I might debug this?