On a site where account activation by an administrator is required, users are informed upon registering that they will receive an email once their account has been activated. This all works out very nicely if the admin activates the user's account by clicking the link given to him in the "Activate user account" email. However, if the admin activates the user through the inactive users section of the ACP, the "account activated" email is not sent to the user.
I searched for this bug before I posted, and I found one just like it, but for phpBB 2.0.20. I can't think of any reason this would be the intended behavior, and several of my friends who use my site have informed me that they didn't know they could log on since they never got the email. Perhaps a small checkbox could be added to the ACP so the admin could choose whether to send the email.