Your problem character, as mentioned in other posts, seems to be Ctrl-Z (between the ± and the á). However I can't reproduce the problem you are having using the sample code below with AS Perl 5.8.7 on Windows XP. Can you make the minimum required changes to the sample code to demonstrate your problem?

use warnings;
use strict;

open outFile, '>', 'test.rsf';
print outFile "ÐÏࡱá                >  þÿ\nThis is plain text";
close outFile;

local @ARGV = ('test.rsf');
local $^I = '.bak';

while (<>)
  {
  chomp;
  print STDOUT (length $_) . " >$_<\n";
  print ">$_<\n";
  }
[download]

Prints:

30 >ÐÏࡱá                >  þÿ<
18 >This is plain text<
[download]