Facebook Graph API - Unable to post feed by app name

I am trying to make an app that has permission to post on user's wall. I have got the publish_stream rights from the user as well as offline access just to make sure. However now when I try to post on the app's subscribers wall using:

$status = $facebook->api("/$user_id/feed", 'POST', array('message' => "$msg"));

However when I do that then instead of posting on subscriber's wall from app it posts from the subscriber's name.

For example, let's say my app name is MyApp and I have a subscriber name Sub1. If, from my interface, I try to post a message 'Test message', it posts on Sub1's wall not by name of MyApp but instead the user himself. Can anyo开发者_如何学编程ne tell me what might be wrong?