I was doing branding in SharePoint 2010 and noticed that SharePoint will render elements declared after a self-closing DIV as children of that DIV. So, if my master page has something like this:

<div style="float: left">Hi world</div>
<div style="clear: both"/>
<div>new section</div>

The page will be rendered as:

<div style="float: left">Hi world</div>
<div style="clear: both">
   <div>new section</div>
</div>

Changing the clear DIV to be <div style=”clear: both”></div> and the page rendered as expected.