XML : Special symbols disappear when using XDocument.Load

As I know, there are several symbols in XML, that should be replaced because they are not valid in pure form in xml:

  < - &lt;  & - &amp;  > - &gt;  " - &quot;  ' - &apos;    

So, I'm trying to load xml document using XDocument.Load(string uri). For example I have in my xml document string that looks like this:

          <net name="&lt;const0&gt;_1"/>    

But when my xml is loaded this string is represented in XDocument as

          <net name="<const0>_1"/>    

I've tried to save it using xdocument.Save(string uri), but in result LT and GT symbols wasn't replaced back with & lt; and & gt; it still looks like < and >. Actually when I loaded it again no exception was thrown. It makes me confused. How could this symbols exist in saved xml file if they are not valid? How can I save my xml file with special symbols replacement? The xml file I'm reading and XDocument I want to save has a declaration with UTF-8 encoding.

Thanks!