REPOST FormsAuthentication.RedirectFromLoginPage is not passed fully qualified url

[Jacob Crossley]

I have two web applications on the same server:

http://localhost/ModemUpgrade

and

http://localhost/TestFormAuth

The web.config of ModemUpgrade:

<authentication mode="Forms">
<forms name=".cuid"
loginUrl="http://localhost/TestFormAuth/MemberLogin.aspx" path="/">
</forms>
</authentication>

PROBLEM:
when I call FormsAuthentication.RedirectFromLoginPage from
MemberLogin.asp,

I notice that ReturnUrl=/ModemUpgrade/Agree.aspx
This keeps me on http://localhost/TestFormAuth/MemberLogin.aspx
because it doesn't have the fully qualified url
(http://localhost/TestFormAuth/Member...://localhost/M
odemUpgrade/Agree.aspx)
needed to complete the redirect

If I manually surf to:
http://localhost/TestFormAuth/Member...ade/Agree.aspx

the whole thing works...Please advise. Thanks.