No, it has definitely not always been there. I've been playing the CMBN and CMFI since they both were released, and this issue never, ever cropped up before the latest patches for both games.
Yes, it is a bug, because before the last update(s) the AI was smart enough to know which side of the wall it should be on. It no longer does. Load up the Biazzo Ridge scenario and watch some of the crazy things the German side (when controlled by the computer) does with its troops when approaching a wall. I dunno how many times it has to be said: it is not just a problem with player-controlled troops.