Notifications and comment approval workflow

I'm having difficulty with notifications and comment approval. Comments posted on my site (version 5.12) require moderator approval before they are published. When someone subscribes to my forum thread, they receive notifications when the author makes updates and when an administrator posts a comment; however, when someone else leaves a comment that requires approval, no notifications are sent out when it's published. I checked the message queue and no messages are created for delivery before or after comment approval.
Am I missing a setting or is this a bug?
Thanks for the help.