It, in the case of your original question, it isn't the fault of S&D, just that you have elected to do a custom scan and to scan memory, which can return unexpected results. e.g. finding unencrypted signatures of other security based applications loaded into memory.
The majority of the issues relating to problems with avast comes from the Teatimer, which can be disabled. But that doesn't take away from the fact that S&D doesn't appear to be keeping pace with modern malware and why MBAM (free) as a secondary on-demand anti-malware scanner to compliment avast.
