Suscribe ticket <creator> to notifications not working

First of all, thanks for this module: It's greatly helpful to me, and the magic of ticket/user creation by email is awesome.

The issue I want to report is as follows:
When a non-user sends a new-ticket-email to a client-mailbox, the ticket gets created and a new-user automatically registered, but this 'external' user doesn't receive any confirmation message nor email notifications when his ticket gets updated.

I have got ticked the 'Prevent user creating or updating ticket from unsubscribing' setting, but seems to have no effect with 'external' users, since they don't get suscribed at all.

Is anyone getting a similar behaviour?

Thanks in advance for any hints to solve this.