If we configure Issue Creation via email and use the option CC Watchers to add CC'ed emails as watchers of the issue, the CC'ed emails are actually added as watchers (if the issue is created successfully), but they aren't notified of the creation of the issue. Only when another event is triggered then will they receive a notification.

The diagnosis is the notification event is fired before the CC'ed emails are added as watchers. This is not an expected behavior as customers would like the CC'ed Watchers to be notified of the creation of the issue.