Newer Kindle models have a setting which turns ON or OFF page refreshes for each page turn. Perhaps Amazon has added that feature to the KK firmware as well. I would check that before sending them all back as what you described sounds like the feature in newer models where the page completely refreshes only after several page turns.

Also, when did they discontinue the KK? It is still listed for sale on the USA website, although only in the 3G configuration.