Properly filtering relationship

[yakatz]

I extended the FreeIPA User to include a relationship:

<?php

namespace App\Ldap\FreeIPA;

use App\Ldap\FreeIPA\Mail\Alias;
use LdapRecord\Models\FreeIPA\User as FreeIPAUser;

class User extends FreeIPAUser
{
    public function aliases()
    {
        return $this->hasMany(Alias::class, 'owner');
    }

}

My Alias model is defined this way:

<?php

namespace App\Ldap\FreeIPA\Mail;

use App\Ldap\FreeIPA\User;
use LdapRecord\Models\FreeIPA\Entry as Model;

class Alias extends Model
{
    public static $objectClasses = [
        'top',
        'mailGroup',
        'groupOfMailEnhancedUniqueNames',
        'mailRecipient',
    ];

    public function owners()
    {
        return $this->hasManyIn(User::class, 'owner');
    }

}

When I try to query for all aliases belonging to a user, I get things which aren't aliases - they don't have the objectClasses that alias is supposed to have - it includes any entry in LDAP that has a matching owner attribute:

$idm_user = IDMUser::findBy('uid', $uid);
$aliases = $idm_user->aliases()->get();

When I inspect the query being run against the LDAP server (using $idm_user->aliases()->getRelationQuery()), it seems to be setting (objectClass=*) in the search.

How do I get it to search the correct entries?