Reported over a week ago at the Google Web Search Help forums, if you use your arrows to navigate up and down the image results on Google Image search, it will skip to the top and bottom.
Here is a video I took myself of showing this in action using the latest version of Chrome on my Mac.
Yesterday, Googler Nathan Beach said, "We can reproduce this and are working to fix it."
There is no estimated time for a fix for this but at least Google knows about it.
Forum discussion at Google Web Search Help.
