I just got a new to me hasselblad cf 150 f4. The problem I am having is every time I take the lens off the camera and put it back in my bag it will fire, then when I put the lens back onto the camera I have to rewind the shutter on the lens. I have never actually seen the lens fire when off the camera and I also can't shake the lens to make it fire. I have two other cf lens and I have never had one of them fire when the lens was off the camera. I just bought this lens off keh. Any idea on why the 150 is doing this?