I see a big difference in your screen shots, but when I tried with something similar—a rock—and took my screenshots—PNGs— with the image at 100%, I'm not seeing it. Looking at a reduced scale isn't ever really accurate, since your aren't displaying 1 image pixel per 1 screen pixel. So maybe that is part of your issue?
I'm sure Chris Cox has a better answer, but my very non-technical understanding is the display at 25% is inaccurate because every time, the software has to make a decision about which of 4 pixels to display or something like that. That's why sharpening is always supposed to be viewed for accuracy at 100%.