grohtml: confused about constant-width font handling

I'm working through some Debian packages whose tests fail with groff 
1.24.0.rc1.  One of those is xlbiff, where there was a previous attempt 
to improve the handling of constant-width font selection in 
https://github.com/edsantiago/xlbiff/commit/e0987fbbcd2304b389f70bbedb9ab9201c8bd7f1.

My current plan is to add the following preamble to the affected pages:

   .ie n .ds CR R
   .el .ds CR CR

... and then just use `.ft \*(CR` in each of the places where it 
currently has a conditional.  This seems to work fine for utf8, ps, and 
pdf output.

However, when I tested with -Thtml I found that the expected <pre> or 
<tt> tag was missing.  I don't exactly remember how this works, so I 
poked around in src/devices/grohtml/post-html.cpp and found this:

   void html_printer::start_font (const char *fontname)
   {
     assert(fontname != 0 /* nullptr */);
     [...]
     } else if (strcmp(fontname, "CR") == 0) {
       if ((! fill_on)
           && is_courier_until_eol()
           && is_line_start(! fill_on)) {
         current_paragraph->do_pre();
       }
       current_paragraph->do_tt();
     [...]
     }
   }

So that should work, right?  CR is meant to turn into a <pre> or <tt> 
tag depending on the context.  But even with current git master, it 
doesn't seem to:

   $ cat t.1
   .TH T 1
   .SH NAME
   t \- a test
   .SH DESCRIPTION
   .ft CR
   constant-width text
   $ ./test-groff -ww -man -Thtml t.1
   [...]
   <p style="margin-left:6%; margin-top: 1em">constant-width
   text</p>

So there's no warning, but also no actual constant-width output.  Am I 
holding it wrong somehow, or is this broken?

Thanks,

-- 
Colin Watson (he/him)                              [[email protected]]