not all keys hash to the same slot for tagged keys, how to fix this

I am trying to call multi-key command "bitOp" with tagged keys, that should be hashed to the same slot.

• php 7.2
• phpredis 3.1.6
• redis_version:5.0.5
• os:Linux 4.15.0-50-generic x86_64
• arch_bits:64

<?php

        $rc = new \RedisCluster(null, $seeds);

        $a = \random_bytes(10000);
        $b = \random_bytes(10000);

        $rc->set('{aaa}a', $a);
        $rc->set('{aaa}b', $b);
        $rc->bitOp('or', '{aaa}c', '{aaa}a', '{aaa}b');

I expect that '{aaa}c' will be created with correct value.

But I get "RedisCluster::bitop(): Warning, not all keys hash to the same slot!"'

Is this a bug somewhere or I am doing something wrong ?