It might be the version difference, I was referencing 4.0.13, or it may be redirecting somewhere else which would take some debugging to see where the redirect is occuring. If you post your login.php maybe I can help.
Alternatively, if you don't want to use your home.php any longer, you could open up your admin/home.php and at the top after <? put:
Code:
header("Location: orders.php"); exit;
This will just redirect to orders.php anytime home.php is loaded, and you can just remove the code to use home.php in the future.