Seems webkit likes to have the background-attachment property explicitly set to "fixed" (as opposed to the default "scroll") for the effect to work.
Code:
body {
margin: 0;
padding: 0;
background: url("../Images/banlv%40k3.jpg");
background-size: contain;
background-repeat: no-repeat;
background-position: 50% 50%;
background-attachment: fixed;
}