The light blue top bar with the buttons "mark forums read, search forums, watched forums, watched threads, new posts" has an issue where if you mouse over any of those buttons, the button moves 'up' a small amount. This specifically causes the issue when your mouse is on the very bottom line of pixels of any off the buttons, because this will cause the button to move up far enough so that you are no longer mousing over it. The button then moves back 'down' to its default position, making it so that you are mousing over it again. This results in the button (and also possibly your mouse icon) rapidly flickering between the two states.
