used to be the opinion that at least in canon cameras, that the raw file was not as for lack of better term, sensitive, and the camera used the jpeg to display on the screen, and you would get the situation you describe, blown highlights in jped and not on raw,,thus you had to know how to set your jpg settings to try an properly determine how you actual histogram would read,, I remember an article over at luminous landscape regarding this several years ago, i don't know if those same parameters exist in the newer technologies.