I have an editing program, called Picture Window Pro, that I’ve only ever used for printing because it is more capable than other things I’ve found for printing more than one image on a single sheet of paper. However, it can produce histograms and it seems to show just what you’ve concluded. In that, on the far right it goes off the chart vertically. While not terribly conspicuous because it is so thin it is there and is consistent with the rest of the histogram.
I’m thinking that GIMP should at least match this one. What about you?
