fix_whitespace_lines: Why does it NOT fix whitespace lines?

[Mike Schleif]

postfix 2.10.1

Why are we getting the following error on some outgoing replies?
    "Improper folded header field made up entirely of whitespace"

# grep fix_w /usr/sbin/amavisd
  my($fix_whitespace_lines, $fix_long_header_lines, $fix_bare_cr) = (0,0,0);
    $fix_whitespace_lines  = 1  if
c('allow_fixing_improper_header_folding');
    $fix_whitespace_lines = 1;  # fix MIME::Entity artifacts
        last  if !$fix_whitespace_lines || $next_head !~ /^[ \t]*\n\z/s;
        if ($fix_whitespace_lines) {  # unfold illegal all-whitespace lines

# grep fix_w /etc/amavisd/amavisd.conf
... EMPTY ...

What am I missing?

~ Mike
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