>
> When I start Emacs and eval these forms in *scratch*, I get:
>
> (mailcap-mime-info "application/pdf")
> "start AcroRd32.exe %s"
>
> (mailcap-mime-info "application/ms-tnef")
> "wmopener.exe \"%s\""
>
> As I'm writing this message, I get:
>
> (mailcap-mime-info "application/pdf")
> doc-view-mode
>
> (mailcap-mime-info "application/ms-tnef")
> nil
>

Indeed.  Patch attached.