Had an issue today with D600 manual mode after every shot I had to adjust the shutter speed which changed after each shot from whatever I set to some new random speed. I had to adjust the shutter back to what I wanted every time. Any ideas what might cause this. I turned off took out Battery restarted. Reset all back to factory setting and adjusted. Nothing changed still same problem. Then it stopped and is not functioning properly? I could have switched something but not aware of what? Anyone experience anything like this?