penders - 5:23 pm on Apr 12, 2013 (gmt 0)
This is the redirect for successful login? You seem to be redirecting to login.php?
Do you have full error reporting set? ie. error_reporting(E_ALL | E_STRICT)
No output (ie. ie HTTP response) is occurring before this that would prevent the header from being set? No BOM? Although that would affect all browsers?!
You could try explicitly setting the HTTP Status code: