Could you show an SSCCE that reproduces the issue? It works fine for me:

use Data::Dump;
use JSON::PP;
my $data = decode_json(q{ { "foo":true, "bar":false } });
dd $data;
my ($foo,$bar) = ($data->{foo},$data->{bar});
print "foo=$foo, bar=$bar\n";
__END__
{
  bar => bless(do{\(my $o = 0)}, "JSON::PP::Boolean"),
  foo => bless(do{\(my $o = 1)}, "JSON::PP::Boolean"),
}
foo=1, bar=0
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Update: You mention "mod JSON", but the above code works for me exactly the same no matter if I do use JSON;, use JSON::XS;, or use JSON::PP;. I also added the Data::Dump output to show these are indeed JSON::PP::Boolean objects.