Until recently, I was running both. After a clean install of Win 7 x64, I noticed Windows defender is disabled by group policy. I see the other threads on this. I am not asking the merits of running both, but what disabled Windows defender, was it the latest version of Avast install?
Use Google to search, not the search build into this webboard software.
You often will get much better results.
e.g. keyword-1 keyword-2 site:forum.avast.com