I read recently that BCIS is trying to come down hard on multiple applications to extend non-immigrant status, if it is done just to prolong the stay (since you can stay till your application is adjudicated, folks are now sending in multiple applications just to keep extending their stay).
So I won't be surprised if BCIS begins to apply that logic to 485 applications too, even if it legal to do so. One never knows these days......even lawyers I hear are perplexed with the current functioning of the immigration system.