Even cameras with mechanical shutters, it seems, aren’t immune to sensor carryover issues. It seems that when you’re doing that famous 8FPS continuous shooting, it’s possible under certain circumstances that a ghost image will be present in the next image shot. Canon says it’s “barely noticeable,” but someone must have noticed anyway because they’re having to issue a fix. It doesn’t occur in single shots or movies; I’m guessing it’s just a timing issue where the sensor isn’t completely reset before the new exposure begins.
In images captured by continuous shooting, and under certain conditions, barely noticeable traces of the immediately preceding frame may be visible. This phenomenon is not noticeable in an image with optimal exposure. The phenomenon may become more noticeable if a retouching process such as level compensation is applied to emphasize the image.
A fix should be here soon, I’d guess within a day or two. In the meantime, those of you with 7Ds should try to replicate it! It sounds kinda cool. I get an effect like that when I’m doing a flash+long exposure and a second flash goes off in the background. It looks crazy as hell. The 7D bug should be nothing like that, but hey.