ASP.Net Form POstback and IIS

I have a website which runs on IIS6.  The homepage for the website is specified in the IIS Documents setting.  The homepage is

Pages/Homepage.aspx?pageId=1512

The home must be in the pages sub dir because this is used by the sites CMS (Ektron) 

The problem I have is that when the homepage is loaded the form tag in the ASP.Net is rendered follows

<form name="aspnetForm" method="post" action="Homepage.aspx?pageid=1512" id="aspnetForm">

This should render as:

<form name="aspnetForm" method="post" action="Pages/Homepage.aspx?pageid=1512" id="aspnetForm">

This problem only happens on the page that is specified in IIS as the home page.  All other pages on the site render fine.

Any ideas?

Thanks Ash......