I keep thinking how can the people at Kobo not know about this defect. It is impossible to see until you are in the exact lighting situation though.
Please tell me you realize how contrary those two statements sound... Do you imagine them subjecting the reader to every type of lighting situation known to mankind and evaluating it from all possible angles? Chances are they looked at them under incandescent and fluorescent lighting from the angles most people would, as well as outdoors, and called it a day. After all they don't produce the e-ink display.
Under exactly what lighting conditions does the problem manifest? What type of bulb(s) or tubes at what angles, etc?