The newest version of Chrome (17.0.963.46) is a bit of a trouble maker – at least on Windows 7 x64. Seems like the border-radius property causes a bug, which fills the background of the element with its borders color – not entirely, but partly at a height of height x ~0,50-0,52.
Deactivating the border-radius seems to “fix” it, and scrolling has also some effects on it.