Pro Site Signup Emails not sent


I have pro sites setup in such a way that I dont have pro site signup on checkout. Meaning users create a free site and have to upgrade later after the site is created.

When the users upgrade later, the process goes fine and I get a green message that You will now receive an email about the upgrade... However no email is sent to the subscriber.

The same subscriber when cancels the subscription gets the email as per the Pro Site Cancelled email setting.

Any ideas as to why the Pro Site Signup emails are no being sent ?