Hello,
They are the same menu but when it floats it gets a new class added to it in the Vertex admin area under "layout > menu". If you want to change its transparent look you can edit that here:
#s5_menu_wrapinner, #s5_topbar_back {
-moz-opacity: 0.43;
-khtml-opacity: 0.43;
filter: alpha(opacity=43);
opacity: 0.43;
position: absolute;
top: 0px;
z-index: 1;
width: 100%;
background: #000;
border-bottom: 1px solid rgba(255, 255, 255, .5);
-webkit-background-clip: padding-box;
background-clip: padding-box;}
template.css line 654