In my established hives I am now using top entrances. In a development that I assume is related to this the bees are clustered in the topmost boxes. The the bottom mediums in each hive still have fair amounts of stores - capped honey, pollen - but also a good bit of mold. Is this a problem? Should it be cleaned off? Similar question regarding stored frames: if there is some capped honey here and there and it has become moldy is this ok to feed back to the bees?
it sounds like its probay just your garden variety mold, so you should be fine just letting the bees clean it off. Bees can be amazingly hygenic with such things. I've had three supers in storage completely mold over, and the bees will clean them our good and fast provided the colony is strong.