Well, I'm wondering how many people see it happening. If it is very common, then there's a reason bees are doing it. Why is that? If I knew that, then I'd know if I wanted to change it, or just accommodate the behavior. At this point, I've left them alone.To correct that, all you need to do is take out the empty top bar(s), move the top bars with combs over near the entrance, then place the empty top bar(s) between other finished combs of brood.