Canon has issued a product advisory for the Powershot A650 IS. Some models are affected by light leakage when using the Variangle LCD in bright sunlight. If this occurs, it will be pretty noticeable on your images. Canon is correcting the issue, free of charge, at their Factory Service Centers.
Image from affected camera (courtesy of Canon)
The problem occurs when you're shooting with the LCD in the open, or folded out, position and the sun is shining on the back of the camera.
A650 IS with LCD in open position(view large image)
The affected cameras have a zero as the fifth digit in the serial number (xxxx0xxxxx). Even if your serial number matches, some models have been corrected already. If they have been serviced, there is a marking underneath the battery cover (see Canon's advisory page, linked below, for more details).
If you don't want to send the camera off for repair, you can simply shoot with the LCD in the closed position.