Hi, first of all, thank you very much for your reply.
The new bug (or the same repeated) was reported by one of our resellers (we are Avast Distributor), is not from a direct customer. We have asked this reseller again and he inform to us that the problem is happening now in 2 of his customers, both with Windows Server 2012. Because of this, and because he was one of the first persons to report this bug months ago, we give value to his words and we believe that it is possible that in some of the latest AfB versions there is a bug (again) with the backup of Windows Server.
Thank you for your tips, we will take them into account. And please, if you do some test with the latest version of AfB, I would appreciate it if you could tell us the result here.