It may be a dub suggest, but i have one problem with my PhaseOne back and mamiya camera; when i mount a lens the back doesn't save in the exif file wich lens it is, because there is a little problem of communication between the camera and the back. I found the solution to this problem, i simply have to change the mode of the camera, for example from M to P and then the camere and the back speak the same language... It's an inexpensive test, try it, maybe this miracle works also for you! I remember that when i discovered this problem i tried everything: i clened the contacts, turned of and on in every different order camera and back, but nothing! Then, i don't know how, i changed the camera's mode and it worked!
Good luck and my best.