I noticed this first with the scrollbars in IE10:
Some user interface elements show the same box as well though. Here is a dropdown box from NetLimiter:
Given that that box looks like the "missing character" symbol used in font rendering, I believe this is somehow related to a font issue. Though I haven't been able to figure this out. The only font I know that's used for UI element rendering is Merlott, and that one looks fine.