The description of the -m option on P2865, L93790 says:
    Stream output format; list files across the page, separated by
    <comma> characters.

The output format for the -m option on P2867, L93858-93860 says:
    When −m is specified, the format used shall be:

    "%s, %s, ...\n", <filename1>, <filename2>

    where the largest number of filenames shall be written without
    exceeding the length of the line.

There are at least two problems here:
1.  The description says that the separator is <comma>, but the output
    format requires that the separator is a <comma> followed by one or
    more <blank> characters.
2.  The output format implies that a filename that is longer than the
    current line length can't be printed.

One implementation I know of prints an empty line before the list of files
when the first filename in the output is longer than the line length.  This
is clearly a bug.

It also always uses a <comma> and a single <space> as a separator with
a <newline> inserted after the separator if printing the following entry
would exceed the line length.  This seems reasonable.  However, some
implementations skip the trailing <space> at the end of a line.  This fix
allows, but does not require the trailing <space>.