* What led up to the situation?

     Checking for defects with a new version

test-[g|n]roff -mandoc -t -K utf8 -rF0 -rHY=0 -rCHECKSTYLE=10 -ww -z < "man page"

  [Use "groff -e ' $' -e '\\~$' <file>" to find obvious trailing spaces.]

  ["test-groff" is a script in the repository for "groff"; is not shipped]
(local copy and "troff" slightly changed by me).

  [The fate of "test-nroff" was decided in groff bug #55941.]

   * What was the outcome of this action?

troff:<stdin>:38: warning: trailing space in the line
troff:<stdin>:41: warning: trailing space in the line
troff:<stdin>:347: warning: trailing space in the line

Bad use of \s0 in a string definition, the string "X" could be resized,
for example with "\s-1\*X\s0".

4:.if t .ds MF M\s-2ETAFONT\s0
8:.if t .ds MF M\s-2ETAFONT\s0
13:.if t .ds BX \fRB\s-2IB\s0\fP\*(TX
16:.if t .ds LX \fRL\\h'-0.36m'\\v'-0.15v'\s-2A\s0\\h'-0.15m'\\v'0.15v'\fP\*(TX
23:.if t .ds WB W\s-2EB\s0

   * What outcome did you expect instead?

     No output (no warnings).

-.-

  General remarks and further material, if a diff-file exist, are in the
attachments.