No, you shouldn't be concerned. Why do you ask?
They are backfilling necter in the brood nest. Have you given them any space?
Which is the way things are supposed to be.
What mistake? I'm confused.
Yes. So, how are you going to address things?
Some hives just take longer to start working the box above. I wouldn't be too concerned unless you can't see any eggs. If that's the case, there may be a problem with the queen.
I would address things by getting rid of those combs with 50% drone cells in them and get them to draw out some new worker combs, do this as soon as all the brood hatches out of them. John
Horseshoe Point Honey -- http://localvahoney.com/
Take the second frame in from each side of the box w/ the drawn comb and replace them w/ frames of foundation from the other box, putting the two drawn comb frames in the upper box in the middle of the upper box, w/ a frame of foundation between them.