background-size: cover not working in portrait on Android tablet

I'm using the background-size property for a full width and height background image but having trouble getting it to fully cover in Chrome on a Nexus7 tablet in portrait view. It only covers the width and not the height i.e. there is about 200px of white space below it. However when I view the site in desktop Chrome (or anything else) and on a vertical monitor to emulate portrait dimensions it covers no problem.

Anyone have a solution?

CSS:

html { 
    background: url(/images/post_bg.jpg) no-repeat center center fixed; 
    -webkit-background-size: cover;
    -moz-background-size: cover;
    -o-background-size: cover;
    background-size: cover;
    -ms-filter: "progid:DXImageTransform.Microsoft.AlphaImageLoader(src='/images/post_bg.jpg', sizingMethod='scale')";
}

Portrait screen shot:

I believe you can fix it by defining the height of the html and body tags in the CSS, like so:

html{
 height:100%;
 min-height:100%;
 }
body{
 min-height:100%;
 }

hope this helps

I know it's been a long time since the question was asked, but I just found the answer I think. For me background-size:cover works in Android Browser and Android Chrome if you omit the "fixed" in the background CSS instruction. After some tests, it works for me making the image the background of a DIV:

#yourDivSelectorHere { 
width: 100%;
height: 100%;  
position: fixed;
top: 0;
left: 0;
z-index: 0; 
background-image: url(/img/backgrounds/1.jpg) ;
background-repeat:no-repeat;
background-position: center center;
/* background-attachment: fixed; removed for Android */
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;

}

The DIV is itself fixed in position (as opposed to the background image), is 100% width and height, and is placed at the back of everything. It's a little extra effort as opposed to just adding the background image to HTML or BODY, but for me it works on all browsers I've tested so far (FF, Chrome, IE8, IE9, Safari), on iPad2 and Android Chrome and Android Browser.