I have now been able to reproduce it on both my test site and your site.
I’ll get Stiofan to look at this.
Scenario:
When a user (user@email) adds a listing and enters an email address for the listing (business@email), GD is sending a confirmation to both email addresses (user@email + business@email).
I guess you do not want an email to be sent to the email address of the listing, but only to the email address of the listing owner.
I think it might be best practice to send confirmation to the listing email address as well, so the business listed knows that their email address has been added to your site; you should not create a contact form for a business unless they know about it (although you can still do this from admin).
So let’s see what the others think about this, and whether this can be made optional.