Creating a pool with workers

I'm slightly baffled by what's happening with my code. I have a number of message queues, and each queue specifies how many workers should be created to process it. Based on that configuration value, I create n instances of my queue worker and add them to the pool. However, when I call getWorkerCount(), I get the wrong value.

// Create a worker pool.
$pool = new ContextWorkerPool(MessageQueueConfig::MAX_WORKERS);
$worker_count = 6;
if ($worker_count < 1) {
  $worker_count = 1;
}
for ($i = 0; $i < $worker_count; $i++) {
  // Create an instance of the queue-specific worker plugin.
  $instance = $this->queueWorkerManager->createInstance('message_queue:' . $queue_config->id());
  dump('Instance created');
  $pool->submit(
    $instance
  );

}
$this->processes[$queue_config->id()] = $pool;
dump('Pool id = ' . $queue_config->id(),  'Worker count = ' . $pool->getWorkerCount(), 'Idle count = ' . $pool->getIdleWorkerCount());

This gives me:

^ "Instance created"
^ "Instance created"
^ "Instance created"
^ "Instance created"
^ "Instance created"
^ "Instance created"
^ "Pool id = immediate"
^ "Limit = 5"
^ "Worker count = 3"
^ "Idle count = 0"

So, definitely creating 6 instances, my limit is 5, so I expected getWorkerCount() to return a value of 5, but it doesn't. It seems that if I create one or two instances, the count is correct, but anything above that only causes that method to return 3.

I'd be grateful for any insight into what's happening!

Start with ContextWorkerPool::submit(), getWorkerCount(), and getIdleWorkerCount(), using the provided six-worker reproduction and pool limit of five. Trace how submitted instances are counted and determine whether the returned count is expected or indicates a defect; done means the discrepancy is explained and, if incorrect, covered by an appropriate regression test.