For my 6x9 Linhof I have an older 6x9 Rollex back. I have a problem with overlaping frames. The overlaping occurs when I don't shot the whole film but carry on maybe one or two weeks later. I never wind until just before I hit the trigger. The "old" frame is then overlapped by approx. 8mm. I can't figure out what causes this. I don't think the film "rewinds" during time by this 8mm. But it seems that the winding of the first frame is to short after a period where the back has not been used? Someone knowing what is going on?