Forms Authentication problem with .Net 4

I'm creating a .Net 4 site using forms authentication and it's not behaving the same way as it did under .Net 2. Here's what I'm doing:
Create a new web application with 3 pages (default.aspx, login.aspx and secure.aspx), this goes into the root folder of a newly created website.
Add the following to the web.config:
<system.web>
  <authentication mode="Forms">
    <forms name=".ASPXFORMSAUTH" loginUrl="~/Login.aspx" slidingExpiration="false" timeout="60" protection="All" />
  </authentication>

  <authorization>
    <deny users="?" />
  </authorization>
</system.web>
<location path="default.aspx"><system.web><authorization><allow users="*" /></authorization></system.web></location>
Let's pretend this website is hosted under test.mysite.dev,the expected behaviour is y ...