To reproduce this, launch apprunner and open a page with a lot of text on it (say, Yahoo!). Click once inside the body of the page to get the blinking insertion mark / caret. Then, press Page Down. What happens is this: first, the screen redraws as it should for a Page Down - and then it redraws again, putting you back up the page. The place where you clicked into the body of the page is now at the very top of the page. Expected behavior would be that you move down the page and the insertion caret disappears, allowing you for example to shift-click on the new area to select a large group of text, etc.

*** This bug has been marked as a duplicate of 3239 ***