Tom, what you described...

yes, I had something similar happen when I was shooting with my Panasonic LX3 in difficult low light conditions... I got lazy and switched the camera to the Intelligent Auto setting. I forgot that the camera then automatically reverts to jpg and adapts the iso accordingly. Result: unpleasant surprise when I came home; limited editing possibilities and more noise than I wished for ;o)

We do not see things as they are. ǝɹɐ ǝʍ sɐ sƃuıɥʇ ǝǝs ǝʍ