I am able to replicate this. I didn’t notice it because I did not test the case of Send me an email when someone quotes me, replies to my post, mentions my @username, or invites me to a topic user pref being enabled. As you can see in Joel’s screenshots, the username of the notifier is correctly displayed. It also displays correctly in the notification menu.
The issue Joel has uncovered is that the display name on email from admin setting, which is enabled by default in discourse, displays the full name of the post author on the email from field.
@dan could it be changed to have the from username in this case to be the notifier, not the post author?