$Storable::drop_utf8 seems ineffective on Perl 5.8.x

[Dan Kogai]

Porters and Storable Maintainers,

       utf8 data
           Perl 5.6 added support for Unicode characters with code  
points >
           255, and Perl 5.8 has full support for Unicode  
characters in hash
           keys.  Perl internally encodes strings with these  
characters using
           utf8, and Storable serializes them as utf8.  By default,  
if an
           older version of Perl encounters a utf8 value it cannot  
represent,
           it will "croak()".  To change this behaviour so that  
Storable dese-
           rializes utf8 encoded values as the string of bytes  
(effectively
           dropping the is_utf8 flag) set $Storable::drop_utf8 to  
some "TRUE"
           value.  This is a form of data loss, because with  
$drop_utf8 true,
           it becomes impossible to tell whether the original data  
was the
           Unicode string, or a series of bytes that happen to be  
valid utf8.

But this does not work as advertised on Perl 5.8.x.

#
use strict;
use warnings;
use Storable qw/dclone/;
my $obj = [ "\x{5c0f}\x{98fc} \x{5f3e}" ];
local ($Storable::drop_utf8) = 1;
my $clone = dclone($obj);
warn utf8::is_utf8($clone->[0]); # not false!
__END__

And here is one of functions in Storable.xs

static SV *retrieve_utf8str(pTHX_ stcxt_t *cxt, char *cname)
{
    SV *sv;

    TRACEME(("retrieve_utf8str"));

    sv = retrieve_scalar(aTHX_ cxt, cname);
    if (sv) {
#ifdef HAS_UTF8_SCALARS
        SvUTF8_on(sv);
#else
        if (cxt->use_bytes < 0)
            cxt->use_bytes
                = (SvTRUE(perl_get_sv("Storable::drop_utf8", TRUE))
                   ? 1 : 0);
        if (cxt->use_bytes == 0)
            UTF8_CROAK();
#endif
    }

    return sv;
}

In other words, $Storable::drop_utf8 is effective iff  
HAS_UTF8_SCALARS is false.  Should we fix the code or documentation?

Dan the Unstorable