We had a lot of cleansing flights "off and on" all Winter into Spring long - it really limits them as a possibility, as Robo said dysentery (or a good case of the trots) running through the hive. Could be a short term problem, something that will cure itself even as more and more activity OUTSIDE of the hive gets your bees away from the hive.
Cells rotate out as brood develop, cleaning continually goes on and eventually everything may be back in balance. Diagnosing other problems is a bit me troubles some, I would keep an eye on them SINCE you say they are behaving fine - but keeping some white cloth nearby to catch flight droppings, maybe photograph them if possible or drawl them out if not.
We (our membership) really needs to compile either our own photos or links to great disease photos for comparison purposes. I've seen so many poor photos on the net showing Foul brood taken from too close and blurry or to far away and not helpful. A data base of ALL good and bad health conditions is a good goal for us to compile - having healthy hive images is JUST as important as bad health issues.
P.S. everyone may have noticed I changed temporarily the logo-photo at the top-left, still looking for a GREAT image to go there, I have been drawing some stuff - not to take GIMP or Paint.net and do the magic :)
On.... and the signature (I just want to let some of the influx of new members catch up with the Admin guy) so there's a bit of info... funny, I though of 4 other hobby things to add, so it's back to the painting board. For the curious, that photo is of me WEARING MY No.17 Matt Kenseth hat while sitting at Dover Speedway in Dover, Delaware.