'Swarming' after honey collecting
My father-in-law is visiting me from Europe. Hi is a beekeeper there. When he collects honey, he shakes bees from the frames infront of hive, and replaces them with empty comb and foundation frames. Bees are coming quickly back into the hive after shaking, but later that day he notices a "beard" of bees, like a swarm, hanging under the hive. He is not able to make them go back into the hive using smoke. And later, he says they go away.
Has anybody noticed that fenomenon? What could be the reason? Are they field bees coming later back home and not let in?