I read about this all the time, but have never personally experienced any film flatness issues w/ 120 cameras. It won't happen if you shoot a red window folder because you get the opportunity to snug the film tight on each frame. If it were going to happen I suspect it would be w/ a TLR, where the film makes a sharp bend before laying in front of the film gate. I live in hot weather climates, and when it's 90+ degrees outside, I suspect that no film emulsion ever made is going to retain a kink in that weather for very long. In cold climates, I could see it theoretically happening. The choice then would be to either burn a frame, or shoot it and see what happens.