output sent and location header

there has been a thread about this topic a couple of days ago, but
nothing was really solved there

http://groups-beta.google.com/group/...148bd281577091

i just stumbled abou the same thing, so i take up the question again.

i have a page that sends output (via session_start(), the cookie is
there) and calls a location header afterwards. against all
expectations it works.

i put a check in

if(!headers_sent())
{
header("Location: URI);
}

but headers_sent() obviously throws FALSE, so the location header is
sent.

any ideas anyone?

micha