Front page login form redirects to wp-login.php

Hi,

When logging using the default login form on the front page of the theme I get redirected to the standard wp-login.php form where I have to reenter the login details to be logged in.

It must be unique to my site setup as I could not see any other posts with the same problem. Does anyone have any idea what I may have wrong?

I have tried turning off all plugins just to be sure. Using the login form on the default BP theme works.

WPMU 3.1.2
BP 1.2.8
Social Theme 1.2.2