Pure nonsense. From Wikipedia, so we are on the same page:
"A heuristic as a noun is a "rule of thumb", an educated guess, an intuitive judgment or simply common sense. A heuristic is a general way of solving a problem". If two programs use the same "rule of thumb" with different length thumbs, there could possible be different results depending on the order. Or had heuristic rules that said opposite things, so you had to decide which one was right. Are there reports that Avast! and MBAM use the same rules with different criteria? As far as my programs, I use Avast! with its "heuristics" along with Prevx which has extreme dependence on heuristics ( see attachment) with absolutely no reason to think they should interfere. And they don't. You may have other reasons for not running MBAM and SAS with Avast! 5, but not because they both use heuristics.