Yes, that is something that changed, it used to be added to your existing expiry date, seems lots of things have been screwed up relating to re-registration, worse for Pro/AIS users as many end up having to get sales to correct the expiry date so they don't lose out.
Whilst avast free users don't lose out as such, it does jar when you get on to it right away only to find the 12 months has effectively become 11, not much of an incentive. I remember the good old days when it was 14 months
