1) Render an image with cameramod set to EV=1.0 and then save this to the history
2) Set the cameramod to EV=2.0 and re-render, then save this to the history
At this point both thumbnails should look correct i.e. one is brighter than the other.
Now make one A and one B and drag the slider around. They look the same. I.e. the image saved in the history is being affected by changes to the cameramod when of course it shouldn't.
Might also happen with other parameters changed in cameramod or even directly in the VFB with no cameramod, I've not tested those.