Yes, it's a known bug but for some reason they haven't fixed it yet.
Same if you try to install Noscript from noscript.net (and other addons through a https connection which are not hosted on AMO) with Avast https scanning enabled.
This annoying bug exists since the first public beta of Avast 2015. I have reported it several times in the German forums section but nothing happened for about 4 months now. Why? It's ridiculous ...