Page jump down not working correctly, very strange, need any advice.

I didn’t see the glitch here (probably because the image is cached), but I have seen a similar one often enough.

On the reasonable assumption that the user prefers not to wait for all the images to download before seeing the text, the browser starts to display the page as soon as it gets any content at all. If the <img> does not contain the image size explicitly, the browser will make a first draft of the page layout with a minimum-size placeholder for the image. If the image is bigger than that placeholder, everything below it must move down – but by then the browser has already scrolled the window to the desired anchor-point, so the adjustment for the image often shifts the desired content down out of view. (Hitting “enter” in the address bar puts it right again.)

Explicit size fields in the <img> ought to prevent this, but I’ve never had occasion to test that solution.