Funny Mojo::JSON FLAGS handling

flagsbug.pl

#!/usr/bin/env perl
use strict;
use warnings;
no warnings 'uninitialized';
use Mojo::JSON;
use Data::Dump 'pp';
use B;
my $data = { 'string' => 'Mojolicious', 'number' => 42, };

# run as:
# perl flagsbug.pl
# perl flagsbug.pl pp
# perl flagsbug.pl num

# The first one is OK, the pp one exhibits the problem,
# the num one shows why the problem appears...

my $flags = B::svref_2object(\$data->{string})->FLAGS;
printf("Original: flags: %08x, SVp_IOK: %08x, SVp_NOK: %08x, flags&(IOK|NOK): %08x\n",
$flags, B::SVp_IOK, B::SVp_NOK, $flags & (B::SVp_IOK | B::SVp_NOK));

if ($ARGV[0] eq "pp") {
        pp($data);
} elsif ($ARGV[0] eq "num") {
        no warnings 'numeric';
        if ($data->{string} + 0 eq $data->{string}) {
                print "String is a number\n";
        } else {
                print "String is not a number\n";
        }
}

$flags = B::svref_2object(\$data->{string})->FLAGS;
printf("Possibly modified: flags: %08x, SVp_IOK: %08x, SVp_NOK: %08x, flags&(IOK|NOK): %08x\n",
$flags, B::SVp_IOK, B::SVp_NOK, $flags & (B::SVp_IOK | B::SVp_NOK));

print Mojo::JSON->new->encode($data), "\n";