Yeah, the questions go on top based on the main thread updated_at timestamp. So no matter if someone replied or made a change in the reply, or you marked an answer as "Best Answer" it always touches updated_at timestamp on the main question and it pops up as latest in the forum.
@joveice, Just to prove a point, you marked the question as "Best Answer" 2 minutes ago. I will modify it now, and the question will again appear on top with reset timer.