I've just had 4 films back from the lab and on each i've lost the first image. It's as if the film hasn't wound on enough and half is the image, and half is black, if you get me. I've never had this happen before, and with these films i only did what i've done with every other film when loading. I always align the arrows on film/camera, i always wind it to start position etc. I've shot 23 rolls in the past 2 months but only these last 4 have ended up like this. I'm on an rb67. Any thoughts on what's gone wrong?