eInk screens naturally behave in this manner, especially if the previous screen had a big contrast to the current screen. In other words, a screen with a lot of black from an image background will probably cause ghosting on a subsequent screen with text. With the K3 you can do a screen refresh (ALT + G) to clear it up. I don't know if the Sonys have a screen refresh option, but page forward then page backward and it should clear up.