In some commands I use this kind of functionality to disable the sending of Emails:
$this->getContainer()->get('event_dispatcher')->removeSubscriber($this->getContainer()->get('my_email_subscriber'));

And then I put it back:

$this->getContainer()->get('event_dispatcher')->addSubscriber($this->getContainer()->get('my_email_subscriber'));

After some debugging I found out that the EventDispatcher now holds closures to enhance LazyLoading in the $this->listeners array.
So the array_search check does not work anymore in function removeListener.

I'm not sure if this really is a bug or if there is a new way now to achieve this.