You can use this code to make a fixed background layer to hack this problem.
#background_wrap {
z-index: -1;
position: fixed;
top: 0;
left: 0;
height: 100%;
width: 100%;
background-size: 100%;
background-image: url('xx.jpg');
background-attachment: fixed;
}
And put <div id="background_wrap"></div>
into <body></body>
<body>
<div id="background_wrap"></div>
</body>