I did notice that underneath the board there was a few white spots. I don't know if this is because that is where it laid on the cardboard as it dried or if it might be a cap issue.
It would be just residue, if you cleaned it more and used distilled water probably would minimise it.. Just wipe it off with isopropyl alcohol. Cap residue I would expect to be at the base of the caps.. I've washed a few boards and its normal to get white spots here and there..
