If you're using IE8, simply press F12, select the browser mode and document mode to IE8.
Next, navigate to any webpage that contains a button with an image overlay. Click on the button and observe how the image moves slightly to the left (-1px) and up (-1px).
This issue can be seen across various websites, such as the search button on bing.com (even though it usually defaults to ie7 document mode) and the select and add to cart buttons on the apple store. It's quite unappealing and appears to only occur when IE8 is set in the mentioned modes.