Hi Stefano,
The reports are always showing 0 for unsubscribed in any "statistics" of any newsletter sent.
Yes, I am using the reports extension.
I have ran tests with both tests subscribers and real newsletters (I first noticed the error with a real newsletter to our real email list of customers). I have ran multiple tests and made sure the subscribers are subscribed before I tested the unsubscribe.
Yes, I use a double step unsubscription. I also have seen an error in a few of my tests where the unsubscribe confirmation page just says "no user found" instead of the "you have now been unsubscribed" goodbye page. This seems to be random though in my tests and I've always made sure my test was done with a confirmed subscriber email.
Thanks,
John