This morning, I had a rude awakening with my Nikon D700. I was shooting in manual and discovered that the ISO did not remain locked at 200. The camera tried to override my exposure decisions by moving the ISO within the range! That is really nasty behavior since Manual should mean MANUAL. What moron thought that this was a good idea?
In the future, I need to remember to switch over to my locked 200 ISO Custom Setting whenever I go into Manual mode. After I discovered the problem, I Googled it and found that Ken Rockwell had given the warning also as a Firmware Defect on the D200 (see Nikon D200 Custom Menu).