If you want for each anchor link to display a different image using one sprite, you have to target each element separately and when setting the background image use top, left to offset the position within the sprite image.
From the link I posted, they have a pretty good example to show how to show different parts of the sprite.
Ok, so you are applying one sprite image to all of the links with no offset. In addition, you set a large value for the height and width. If you take a look at the example that the w3schools has on their site, you'll notice that they apply a different style to each link, then add an offset so that each link has a portion of the sprite's background.
In your example, you get six images due to the height of 151. Your image repeats itself within that height.
ok, I shall have a wild guess in this case. It maybe cause as the image have repeat itself as the width of the link is set wider than the image.
First solution is reduce the width of the link and another is to set the background-repeat: no-repeat;