->id created as accessor even though no id column - feature? bug?

id_or_foo_id.pl

{
    package SomeResult;
    use strict;
    use warnings;
    use base 'DBIx::Class::Core';

    __PACKAGE__->table("foo");
    __PACKAGE__->add_columns(
        foo_id => {
            data_type => "integer",
            is_auto_increment => 1
        },
        name => {
            data_type => "char",
            is_nullable => 1
        },
    );
    __PACKAGE__->set_primary_key("foo_id");
}
{
    package SomeSchema;
    use base "DBIx::Class::Schema";
    __PACKAGE__->register_class( SomeResult => "SomeResult" );
}

my $s = SomeSchema->connect("DBI:SQLite:dbname=:memory:");
$s->deploy;
my $obj = $s->resultset("SomeResult")->create({ name => "Simon" });

print "foo_id: " . $obj->foo_id . "\n";
print "    id: " . $obj->id . "\n";

Feature. Defined in DBIx::Class::PK