Just adding on to this.....
I am seeing the same issue.
However it seems that in my instance it occurs when I have an "on open action" that copies a subscriber to a different list.
In the campaign overview the 'List Segment' confirmed subscriber count only includes subscribers with a 'confirmed' status and not those that did receive the email but now have a 'moved' status despite still belonging to the original list.
Thus the Recipient count
$campaign->stats->getDeliverySuccessCount(true) is greater than the List subscriber count
$campaign->stats->getSubscribersCount(true)
Not a massive issue for me but is there a simple way to get around this?
