The wallpaper list seems to be in two segments - the first set of plain gradients and the second set of photos. I find that when I scroll through the list the background doesn't change (for a preview) when I go from the top half of the list to the bottom half, until I actually reach the very bottom, and vice versa. For example, if I'm at the top of the list (Sun Rise) and scroll down the display updates properly until Stone, but it stays grey until I get to the bottom (Weathered Wood) when it updates to that image. If I then go back up it works fine until I get to Amber, which sticks until I get back up to Sun Rise.