I don't see the problem. 

use strict;
use warnings;

use Data::Dumper qw( Dumper );

$Data::Dumper::Useqq  = 1;
$Data::Dumper::Terse  = 1;
$Data::Dumper::Indent = 0;

my $s = chr(0xC9);
utf8::downgrade($s);
print(Dumper(unpack('H*', $s)), "\n");
utf8::upgrade($s);
print(Dumper(unpack('H*', $s)), "\n");

print(Dumper(unpack('H*', "\x{C9}\x{2660}")), "\n");

[download]

5.10.0: 

"c9"        # Ok
"c9"        # Ok
Character in 'H' format wrapped in unpack at 750077.pl line 16.
"c960"      # GIGO

[download]

The internal representation is and should be irrelevant.

If you want to see the internal representation, it stands to reason that you should have to explicitely fetch it.

In reply to Re^3: Understanding pack and unpack changes for binary data between 5.8 and 5.10 by ikegami
in thread Understanding pack and unpack changes for binary data between 5.8 and 5.10 by dkg

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