I modified Layers.pm to dump the flags. 
sub _has_flags {
    my $check_flag = _names_to_flags(@_);
    return sub {
        my ($fh, $layer) = @_;
        my $iterator = natatime(3, PerlIO::get_layers($fh, details => 
+1));
        while (my ($name, $arguments, $flags) = $iterator->()) {
            next if defined $layer and $name ne $layer;
            print('FL='.unpack('H8',pack('N',$flags)).','.unpack('B32'
+,pack('N',$flags))."\n");
            print('CK='.unpack('H8',pack('N',$check_flag)).','.unpack(
+'B32',pack('N',$check_flag))."\n");
            my $entry = $flags & $check_flag;
            return 1 if $entry;
        }
        return 0;
    }
}

[download]
And the problem is, 5.10 has different flags than 5.12. I dont know yet if 5.10 has different C consts, or just different api design, and if the 16XXX/0x4000 flag is plain wrong. I havent looked if 0x4000 is hard coded in Layers the module or not.

On 5.10. 
$VAR1 = {
          "\$mode" => "<:encoding(utf8)",
          "\$fh" => \*{"main::\$fh"},
          "\$test_type" => "crlf",
          "\$result_for{\$test_type}" => 1
        };
FL=00408400,00000000010000001000010000000000
CK=00004000,00000000000000000100000000000000
FL=00408400,00000000010000001000010000000000
CK=00004000,00000000000000000100000000000000
FL=00408400,00000000010000001000010000000000
CK=00004000,00000000000000000100000000000000
not ok 51 - File opened with <:encoding(utf8) should return 1 on test 
+crlf
#   Failed test 'File opened with <:encoding(utf8) should return 1 on 
+test crlf'
#   at 10-basics.t line 77.
#          got: '0'
#     expected: '1'
# $VAR1 = [
#           "unix",
#           undef,
#           [
#             "UTF8",
#             "CANREAD",
#             "FASTGETS"
#           ]
#         ];
# $VAR2 = [
#           "crlf",
#           undef,
#           [
#             "UTF8",
#             "CANREAD",
#             "FASTGETS"
#           ]
#         ];
# $VAR3 = [
#           "encoding",
#           "utf8",
#           [
#             "UTF8",
#             "CANREAD",
#             "FASTGETS"
#           ]
#         ];

[download]
On 5.12 
$VAR1 = {
          "\$fh" => \*{"main::\$fh"},
          "\$mode" => "<:encoding(utf8)",
          "\$result_for{\$test_type}" => 1,
          "\$test_type" => "crlf"
        };
FL=00200400,00000000001000000000010000000000
CK=00004000,00000000000000000100000000000000
FL=00404400,00000000010000000100010000000000
CK=00004000,00000000000000000100000000000000

[download]
I will keep looking.

I made this. Dont know what to think about it. http://pastebin.com/SSDrPpDD

update, the flags come from XS in Layers.xs not hard coded consts in the PM, the flags of the layers come from http://perl5.git.perl.org/perl.git/blob/HEAD:/universal.c#l960 I dont have a C debugging enabled 5.10 so I cant give you any more advice. Search perlio.c in perl.git for changes between 5.10 and 5.12 or dont do the PIO::Layers test on 5.10. Its a design issue with 5.10, not a Layers.pm issue.

In reply to Re^3: [Win32] PerlIO-Layers fails 4 tests on perl-5.10 only by bulk88
in thread [Win32] PerlIO-Layers fails 4 tests on perl-5.10 only by syphilis

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