Tip #6 from the Basic debugging checklist: B::Deparse:

use warnings;
use strict 'refs';
'STDOUT'->say('like a charm');
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Not that I know what that means, but it is a clue.

Also, when I run the code on 5.12, I get an error:

Can't locate object method "say" via package "IO::File" at ...
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It's the indirect method call syntax. Your code is interpreted as:

use strict;
use warnings;

STDOUT->say('like a charm');
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So you're not using the say keyword; you're using the say method in IO::Handle.

lanx@nc10-ubuntu:~$ perl
use strict;
use warnings;

say STDOUT 'like a charm';
Can't locate object method "say" via package "IO::Handle" at - line 4.
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But the last line should lead to the answer.

print FH is (supposed to be) indirect object syntax of the filehandle-object, so somehow the method say was activated by default in your environment.

Anyway calling say w/o FH shouldn't work!

This is because of a change in Perl 5.14:

Filehandle method calls load IO::File on demand

The OP's code does work in Perl 5.10, if you run it with the -MIO::Handle parameter to manually load the IO::Handle package.

package Cow { use Moo; has name => (is => 'lazy', default => sub { 'Mooington' }) } say Cow->new->name

So print FH was magic in doing so prior to 5.14?

I hate breakes in symmetry...

BTW: I checked IO::Handle , it's a normal method and features aren't checked.

sub say {
    @_ or croak 'usage: $io->say(ARGS)';
    my $this = shift;
    local $\ = "\n";
    print $this @_;
}
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Cheers Rolf