Omitting most of the script

That requires that I omit most of my diagnosis. :)

No, // won't matter. Also, contrary to the HTML specification, not even -- matters (as far as PerlMonks is concerned "HTML comments" simply start with <!-- and end with -->).

Since you don't give me much to work with, I'll give you the code (that manipulates the contents of the Free Nodelet) and you can diagnose the problem:

$html =~ s{`([\[\]]|`+|(\w+)([%&\\]?)`?|.)}{
    my $s= $1;
    if(  '[' eq $s  ) {
        $just ? '[' : '`{';
    } elsif(  ']' eq $s  ) {
        $just ? ']' : '`}';
    } elsif(  defined $2  ) {
        my( $key, $suff )= ( $2, $3 );
        my $val;
        if(  $key =~ /^_./  ) {
            $val= $q->param($key);
            $val= $q->param( substr($key,1) )
                if  ! defined $val;
        } else {
            $key =~ s/_name$/_title/i;
            $val= $var{ lc $key };
        }
        if(  ! defined $val  ) {
            $val= "`$key$suff`"
        } elsif(  $suff eq '%'  ) {
            $val= $q->escape($val);
        } elsif(  $suff eq '&'  ) {
            $val= $q->escapeHTML($val);
        } elsif(  $suff eq '\\'  ) {
            $val=~ s/(['"\\])/\\$1/g;
        }
        $val;
    } elsif(  $s =~ /^`/  ) {
        $just ? $s : '`'.$s;
    } else {
        $just ? '`'.$s : '``'.$s;
    }
}seg;

return $html   if  $just;

$html =~ s{(<!--.*?-->)|\[([^\[\]]{1,4096})\]}{
    $1 ? $1 : handleLinks($2)
}seg;

$html =~ s{`([{}]|`+|.)}{
    my $s= $1;
    if(  '{' eq $s  ) {
        '[';
    } elsif(  '}' eq $s  ) {
        ']';
    } elsif(  $s =~ /^`/  ) {
        $s;
    } else {
        '`'.$s;
    }
}seg;
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