Corrupted? Hardly. Changed? Yes. What it really means is that you are working the image, making adjustments to various parts of it. It shouldn't be surprising that the HSV of the pixels changes in interesting and odd ways according to the histogram. The test of corruption IMHO is the print -- are your adjustments to the image leaving visible artifacts? If they are then a smooth histogram won't help you. If they aren't then a choppy histogram isn't something to worry about.
That said I fully agree that it is very important that one start with the best possible image capture and best possible scan (if film). Image editors can do interesting and sometimes amazing things, but they can not create new information -- just new data.
It's perfectly possible to work in 8 bit spaces but it really puts a premium on the quality of the image capture and scan. It's much easier to get good results when working in 16 bit -- more headroom makes it easier to maneuver.
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