I got the same problem.
Your idea of Z-axis give me the idea of checking the Z-index in the CSS files.
In your Style.css file of your theme or your child theme, you can find an entry with branding as the name :
#branding {
border-top: 2px solid #bbb;
padding-bottom: 10px;
position: relative;
z-index: 9999 ;
}
Change the z-index entry with
z-index: 1;
Then in the header.php file of your theme or of your child theme search the first line with body. Something like this :
<body <?php body_class(); ?>>
<div id="page" class="hfeed">
Add a style argument to set the Z-index value to a very high value:
<body <?php body_class(); ?>>
<div id=”page” class=”hfeed” style=”z-index:9999;”>
This works for me with a child theme based on Twenty Eleven.
Regards