Why is inline style being added to DIV in ASP.NET 4.0?

Why is inline style being added to DIV in ASP.NET 4.0?

I have a normal LI type menu in a project I am starting on. But somehow an
inline css float: left rule is being added.
What causes this?
<div id="dolphinnav" style="float: left; cssfloat: left;"
Sys.WebForms.Menu.Mapping="dolphinnav"...