In this case they are awsome then, one of my cories feed that way last night, but it was cause they put the wafer behind a plant and the only way he finds to eat it was upside down.
I've seen Corydoras taking food from the surface, and even searching the surface for food (C.agassizi seem the most interested in such activities among the cories I have), but no "real" cory approached these chaps...
They are even more pathological now... when then know that feeding is approaching, they start the upside-down swimming.