Lordy. I opened up my (going to be replaced due to clouds/splotches) unit, and tried to think of a good test. I have a bunch of cookbooks with photos (I usually read these with the kindle app on my ipad, don't get me wrong), so I loaded one up to see if I had any light spots.
No, but on page illustrations (photos), in the darker areas of the image I can clearly see (clear enough to read) the ghosted/inverted image of whatever text was on the previously-rendered page. This is with Page Refresh on. I'm pretty sure my KK didn't do this, the few times I looked through a cookbook or other book with photos, but now I'll have to check when I get home. (Sorry if this is sort of a thread derailment--but would anyone else like to check a book with photos (or possibly just the cover image) and tell me if the same thing happens?)