I can only guess (but I've done graphics programming so its at least an educated guess), but in this particular case it looks like its happening because of an optimization with the background. When the camera is staying at the same angle, the background stays exactly the same, so instead of wasting time clearing and redrawing the background every frame its only redrawing it if the camera moves. This is fine in normal gameplay because of the limited camera controls but when you go out of bounds it causes other elements (like the motorcycle) to also not be properly cleared until the camera moves, creating the effect you see above.

Again, this is just a guess, but based on observation and my experience I think it's a pretty reasonable guess.