I was thinking more about cache of Avast - when it blocks something and sees it for the second time in a short while, it blocks it automatically without actually checking it. Of course this "short while" is set for a sufficient short amount of time: after a couple of minutes (?) the cache is invalidated. Perhaps there is a bug that prevented invalidating Avast cache in your specific case, therefore Avast didn't bother to check if it is blocked and fetched last result, which is "block this URL".
I am glad this is now resolved ;-)!
