It appears that the larva had inadvertently dropped near the mouth of the orignal cell, so the bees just made the cell longer. normally the larva should sit near the bottom of the cell, but because all queen cells point upwards, I suppose gravity sometimes plays tricks with bees also. The cell on right, on the other hand, appeared to be too small. Several of these sealed cells had a tiny larva in them. Not sure what is wrong. It is possible that workers have used drone larvae for emergency cells, since all other brood closeby are drones.