It has happened only once to me in approx. 500 photos total I've taken. I was inside with my back to a window, decent amount of daylight coming in. I was playing with the panorama assist mode. There was a stripe of blotching on the right side of the frame and was clearly visible on the lcd before I took the shot, (Class 6 card.)
DolnaM, I know this is a bit of a silly question since you were using sunset mode, but can you confirm you were outside when it happened to you?