Anyway, I updated my test program to something that should now replicate your error: 
use strict;
use warnings;
use Devel::Peek 'Dump';
my $token = "ba\x{f1}o";
utf8::upgrade($token);  # force utf-8 encoding and flag.

my $term = "ba\303\261o"; # "utf-8 encoded" but no flag.

warn "Token:\n";
Dump($token);

warn "Term:\n";
Dump($term);

print "match\n" if $token =~ /^$term/i;

[download]
Note that this runs fine (i.e. no match, no error) on my system (5.8.8 built for i686-linux-thread-multi).

"What should it profit a man, if he should win a flame war, yet lose his cool?"

In reply to Re^7: Malformed UTF-8 by Joost
in thread Malformed UTF-8 by spiros

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