Where does this extra space comes from?

Where does this extra space comes from?

As you can see here http://jsfiddle.net/FqW4R/ and on the picture below,
my menu items are not perfectly aligned with "logo" and "social". Also
there's a massive gap between the menu categories (Menu I, Menu 2, etc)
and the sub-items. When I look at my code I do not see extra padding or
anything like that that could cause this type of issue. Any thoughts on
that? Many thanks

Html, body {
margin: 0;
padding: 0;
background: #fff;
font-family: 'Open Sans', sans-serif;
}
#logo {
position: absolute;
top: 35px;
left: 20px;
color: #000;
font-size: 20px;
}
/* mainmenu */
#mainmenu {
float:right;
margin-top: 35px;
padding-bottom: 10px;
overflow: hidden;
}
#mainmenu ul {
float: right;
margin: 0;
color: #000;
list-style: none;
}
#mainmenu ul li {
display: inline-block;
float: left;
width: 140px;
line-height: 20px;
}
#mainmenu>ul>li {
margin-left: 20px;
}
#mainmenu ul li a {
display: block;
text-decoration: none;
font-weight:600;
font-size: 12px;
}
#mainmenu ul li a, #mainmenu ul ul:hover li a {
color: #333;
-webkit-transition-timing-function: ease-out, ease-in, linear,
ease-in-out;
-moz-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-ms-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-o-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-webkit-transition-duration: .4s, .4s, .4s, .4s;
-moz-transition-duration: .4s, .4s, .4s, .4s;
-ms-transition-duration: .4s, .4s, .4s, .4s;
-o-transition-duration: .4s, .4s, .4s, .4s;
transition-duration: .4s, .4s, .4s, .4s;
-webkit-transition-property: all, -webkit-transform;
-moz-transition-property: all, -moz-transform;
-ms-transition-property: all, -ms-transform;
-o-transition-property: all, -o-transform;
transition-property: all, transform;
}
#mainmenu ul ul li a:hover, #mainmenu ul ul li.current-menu-item a {
color: #005EBC;
-webkit-transition-timing-function: ease-out, ease-in, linear,
ease-in-out;
-moz-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-ms-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-o-transition-timing-function: ease-out, ease-in, linear, ease-in-out;
transition-timing-function: ease-out, ease-in, linear, ease-in-out;
-webkit-transition-duration: .4s, .4s, .4s, .4s;
-moz-transition-duration: .4s, .4s, .4s, .4s;
-ms-transition-duration: .4s, .4s, .4s, .4s;
-o-transition-duration: .4s, .4s, .4s, .4s;
transition-duration: .4s, .4s, .4s, .4s;
-webkit-transition-property: all, -webkit-transform;
-moz-transition-property: all, -moz-transform;
-ms-transition-property: all, -ms-transform;
-o-transition-property: all, -o-transform;
transition-property: all, transform;
}
#social {
position: absolute;
float:right;
right: 10px;
Color: blue;
margin-top: 35px;
}
HTML
<div id="logo">Logo</div> <!-- End DIV Logo -->
<div id="mainmenu">
<ul>
<li>
<h5>Menu I</h5>
<ul>
<li><a title="" href="">Biography</a> </li>
<li><a title="" href="">Publications</a> </li>
</ul>
<li>
<h5>Menu 2</h5>
<ul>
<li><a title="" href="">Demo</a> </li>
<li><a title="" href="">Features</a> </li>
<li><a title="" href="">Comparison</a> </li>
</ul>
</li>
<li>
<h5>Menu 3</h5>
<ul>
<li><a title="" href="">Item 1</a> </li>
<li><a title="" href="">Item 2</a> </li>
<li><a title="" href="">Item 3</a> </li>
</ul>
</li>
<li>
<h5>Menu 4</h5>
<ul>
<li><a title="" href="">ddfd</a> </li>
<li><a title="" href="">dsfd</a> </li>
</ul>
</li>
</ul>
</div> <!-- End DIV Main Menu -->
<div id="social">Social</div><!-- End DIV Social -->