Maybe you need to upgrade lwp/mechanize/base64 to the latest

#!/usr/bin/perl --

use strict;
use warnings;

use WWW::Mechanize;
use MIME::Base64;
print "

WWW::Mechanize $WWW::Mechanize::VERSION
MIME::Base64 $MIME::Base64::VERSION
LWP $LWP::VERSION

";
__END__

WWW::Mechanize 1.34
MIME::Base64 3.05
LWP 5.814
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