I am experiencing the same issue - my theory is that by some reason the settings are being reverted (perhaps after an update).
Could someone provide the path to template? (I am using Win10 and Avast 11.1).
BTW: Disable is not the answer. Who has allowed the Avast to manipulate a text of message and add the signature!? I was compromised when a professional e-mail, sent via a www-based client, was ended with an Avast signature, furthermore - a signature in Polish! Yes, I have set my Avast to Polish but never use that language at work! Unacceptable! Shame on you, the Business Manager, who has allowed to develop such an offensive feature!