Hello all I recently purchased a mamiya RB67 Pro S with two backs, one is a Pro S back the other is a Pro SD back. I have encountered one tiny issue and while it's not that big of a deal it would be nice if I could find the problem. The Pro S back works absolutely perfectly, but when using the Pro SD back in portrait orientation the red marker does not move into place after a shot has been fired and I have to flip the little lever on the back to be able to advance the film. It doesn't seem to matter where I set the double exposure switch and it only does it with the back in portrait orientation, all is fine in landscape. Anyone ever seen this before? As I said it's not a big deal but figuring it out would eliminate an extra step.