What's the output of the following?

use strict;
use warnings;

use Params::Validate
    qw( validate validate_pos UNDEF SCALAR BOOLEAN HASHREF OBJECT );

print($INC{'Params/ValidateXS.pm'} ?'XS':'PP',"\n");

    my $spec = {
        epoch     => { regex => qr/^-?(?:\d+(?:\.\d*)?|\.\d+)$/ },
        locale    => { type  => SCALAR | OBJECT, optional => 1 },
        language  => { type  => SCALAR | OBJECT, optional => 1 },
        time_zone => { type  => SCALAR | OBJECT, optional => 1 },
        formatter => {
            type     => SCALAR | OBJECT, can => 'format_datetime',
            optional => 1
        },
    };

use Devel::Peek;
Dump($spec->{epoch}{regex});
my $x = $spec->{epoch}{regex};
Dump($spec->{epoch}{regex});

validate( @{[ 'epoch', 1301690690 ]}, $spec );
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XS SV = IV(0xa26f58) at 0xa26f60 REFCNT = 1 FLAGS = (ROK) RV = 0xa26f48 SV = REGEXP(0xa67418) at 0xa26f48 REFCNT = 1 FLAGS = (OBJECT,POK,FAKE,pPOK) IV = 0 PV = 0xa75e90 "(?-xism:^-?(?:\\d+(?:\\.\\d*)?|\\.\\d+)$)" CUR = 36 LEN = 0 STASH = 0xa0b8f0 "Regexp" SV = IV(0xa26f58) at 0xa26f60 REFCNT = 1 FLAGS = (ROK) RV = 0xa26f48 SV = REGEXP(0xa67418) at 0xa26f48 REFCNT = 2 FLAGS = (OBJECT,POK,FAKE,pPOK) IV = 0 PV = 0xa75e90 "(?-xism:^-?(?:\\d+(?:\\.\\d*)?|\\.\\d+)$)" CUR = 36 LEN = 0 STASH = 0xa0b8f0 "Regexp" 'regex' validation parameter for 'N/A must be a string or qr// regex at monktest.pl line 25

Identical to me. I don't know how you could be getting that error. The code in question is

    if ((temp = hv_fetch(spec, "regex", 5, 0))) {
        dSP;

        IV has_regex = 0;
        IV ok;

        SvGETMAGIC(*temp);
        if (SvPOK(*temp)) {
            has_regex = 1;
        }
        else if (SvROK(*temp)) {
            SV* svp;

            svp = (SV*)SvRV(*temp);

            #if PERL_VERSION <= 10
            if (SvMAGICAL(svp) && mg_find(svp, PERL_MAGIC_qr)) {
                has_regex = 1;
            }
            #else
            if (SvTYPE(svp) == SVt_REGEXP) {
                has_regex = 1;
            }
            #endif
        }

        if (!has_regex) {
            SV* buffer;

            buffer = sv_2mortal(newSVpv("'regex' validation parameter 
+for '", 0));
            sv_catsv(buffer, get_called(options));
            sv_catpv(buffer, " must be a string or qr// regex\n");
            FAIL(buffer, options);
        }
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You can probably get around the problem by using the pure Perl backend. You can do that by setting environment variable PV_TEST_PERL to something true.

PV_TEST_PERL=1 perl script.pl
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or

BEGIN { $ENV{PV_TEST_PERL} = 1; }
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Tried with the same result, thanks for all the the help so far though