Random and Erroneous WordPress Redirect

If the redirect comes from WordPress code, you can find out who is calling wp_redirect() by hooking into it:

add_filter( 'wp_redirect', 'wpse12721_wp_redirect' );
function wpse12721_wp_redirect( $location )
{
    // Get a backtrace of who called us
    debug_print_backtrace();
    // Cancel the redirect
    return false;
}