I think the movement of the histogram between these 2 files is due to the rendering intent. When a sRGB file is loaded the file is transformed to the AdobeRGB color space. Since this is a bigger one only the pixel values are changed to gain exact the same colors. But once in memory what is seen is sRGB. That same file is now transformed to sRGB using perceptual rendering intent. All the colors are shifting a little. And to the right of the histogram.
George