update: ignore this, I misread the start of the script :-(

Is argument 6 @ff? If so it looks as though it is getting clobbered when you "determine the field names".

  # determine the field names
  if ($colNamesHdl) {
    @ff=();
    for ($i=0; $i <= $#$colNamesHdl; $i++) {
      push(@ff, $$colNamesHdl[$i]);
    }

  } else {
    $k  = $$rowsHdl[0];
    @ff = keys(%$k);
  }
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Either unshift the field names onto @ff or perhaps just print the field names outside your for loop and leave @ff well alone.

update: changed shift to unshift